diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7e26168..bcb728d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,7 +9,8 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ["2.7", "3.0", "3.1", "3.2", "3.3"]
+        ruby-version: ["3.0", "3.1", "3.2", "3.3"]
+        activesupport-version: ["activesupport-6.1", "activesupport-7.1"]
 
     steps:
       - uses: actions/checkout@v4
@@ -18,9 +19,11 @@ jobs:
       - uses: actions/cache@v4
         with:
           path: vendor/bundle
-          key: ${{ runner.os }}-gems-${{ hashFiles('**/Gemfile.lock') }}-v1
+          key: ${{ runner.os }}-gems-${{ hashFiles('**/Gemfile.lock') }}-v2
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby-version }}
       - run: bin/setup
-      - run: bin/test
+      - run: bundle exec appraisal generate
+      - run: bundle exec appraisal install
+      - run: bundle exec appraisal ${{ matrix.activesupport-version }} bin/test
diff --git a/Appraisals b/Appraisals
index f1ed289..2538f07 100644
--- a/Appraisals
+++ b/Appraisals
@@ -1,14 +1,7 @@
-appraise "ruby-2.7" do
+appraise "activesupport-6.1" do
+  gem "activesupport", "~> 6.1.0"
 end
 
-appraise "ruby-3.0" do
-end
-
-appraise "ruby-3.1" do
-end
-
-appraise "ruby-3.2" do
-end
-
-appraise "ruby-3.3" do
+appraise "activesupport-7.1" do
+  gem "activesupport", "~> 7.1.0"
 end
diff --git a/Gemfile b/Gemfile
index 3be9c3c..a505cf2 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,2 +1,4 @@
 source "https://rubygems.org"
 gemspec
+
+gem "activesupport", ">= 5.1"
diff --git a/bin/test b/bin/test
index fbf51fa..b49e77d 100755
--- a/bin/test
+++ b/bin/test
@@ -1,4 +1,5 @@
 #!/bin/sh
 
 echo "== Running tests =="
+[ "${CI}" = "1" ] && bundle info activesupport
 bundle exec rake test "$@"
diff --git a/test/cases/time_slice_test.rb b/test/cases/time_slice_test.rb
index ced55f6..cf28577 100644
--- a/test/cases/time_slice_test.rb
+++ b/test/cases/time_slice_test.rb
@@ -12,61 +12,61 @@ class TimeSliceTest < TestCase
   it "accepts a period and :length option" do
     range = TimeSlice.new("2h", length: "4")
     assert_equal 4, range.length
-    assert_equal "2019-01-06 10:00:00", range.from.to_fs(:db)
-    assert_equal "2019-01-06 16:00:00", range.to.to_fs(:db)
-    assert_time_range "[2019-01-06 10:00:00, 2019-01-06 12:00:00]", range[0]
-    assert_time_range "[2019-01-06 12:00:00, 2019-01-06 14:00:00]", range[1]
-    assert_time_range "[2019-01-06 14:00:00, 2019-01-06 16:00:00]", range[2]
-    assert_time_range "[2019-01-06 16:00:00, 2019-01-06 18:00:00]", range[3]
+    assert_equal "2019-01-06T10:00:00Z", range.from.iso8601
+    assert_equal "2019-01-06T16:00:00Z", range.to.iso8601
+    assert_time_range "[2019-01-06T10:00:00Z, 2019-01-06T12:00:00Z]", range[0]
+    assert_time_range "[2019-01-06T12:00:00Z, 2019-01-06T14:00:00Z]", range[1]
+    assert_time_range "[2019-01-06T14:00:00Z, 2019-01-06T16:00:00Z]", range[2]
+    assert_time_range "[2019-01-06T16:00:00Z, 2019-01-06T18:00:00Z]", range[3]
 
     range = TimeSlice.new("2h", length: 1)
     assert_equal 1, range.length
-    assert_time_range "[2019-01-06 16:00:00, 2019-01-06 18:00:00]", range[0]
+    assert_time_range "[2019-01-06T16:00:00Z, 2019-01-06T18:00:00Z]", range[0]
   end
 
   it "is enumerable" do
     assert range.each { true }
-    assert_time_range "[[2019-01-06 14:00:00, 2019-01-06 16:00:00], [2019-01-06 16:00:00, 2019-01-06 18:00:00]]", range
+    assert_time_range "[[2019-01-06T14:00:00Z, 2019-01-06T16:00:00Z], [2019-01-06T16:00:00Z, 2019-01-06T18:00:00Z]]", range
   end
 
   it "accepts a :from option" do
     range = TimeSlice.new("5m", from: "2019-01-06 17:20")
-    assert_equal "2019-01-06 17:20:00", range.from.to_fs(:db)
-    assert_equal "2019-01-06 17:40:00", range.to.to_fs(:db)
-    assert_time_range "[2019-01-06 17:20:00, 2019-01-06 17:25:00]", range.first
-    assert_time_range "[2019-01-06 17:40:00, 2019-01-06 17:45:00]", range.last
+    assert_equal "2019-01-06T17:20:00Z", range.from.iso8601
+    assert_equal "2019-01-06T17:40:00Z", range.to.iso8601
+    assert_time_range "[2019-01-06T17:20:00Z, 2019-01-06T17:25:00Z]", range.first
+    assert_time_range "[2019-01-06T17:40:00Z, 2019-01-06T17:45:00Z]", range.last
     assert_equal 5, range.length
 
     range = TimeSlice.new("1m", from: "2019-01-06 17:20")
-    assert_equal "2019-01-06 17:20:00", range.from.to_fs(:db)
-    assert_equal "2019-01-06 17:44:00", range.to.to_fs(:db)
-    assert_time_range "[2019-01-06 17:20:00, 2019-01-06 17:21:00]", range.first
-    assert_time_range "[2019-01-06 17:44:00, 2019-01-06 17:45:00]", range.last
+    assert_equal "2019-01-06T17:20:00Z", range.from.iso8601
+    assert_equal "2019-01-06T17:44:00Z", range.to.iso8601
+    assert_time_range "[2019-01-06T17:20:00Z, 2019-01-06T17:21:00Z]", range.first
+    assert_time_range "[2019-01-06T17:44:00Z, 2019-01-06T17:45:00Z]", range.last
     assert_equal 25, range.length
   end
 
   it "accepts a :from and :to option" do
     range = TimeSlice.new("5m", from: "2019-01-06 17:10", to: "2019-01-06 17:35")
-    assert_equal "2019-01-06 17:10:00", range.from.to_fs(:db)
-    assert_equal "2019-01-06 17:35:00", range.to.to_fs(:db)
-    assert_time_range "[2019-01-06 17:10:00, 2019-01-06 17:15:00]", range.first
-    assert_time_range "[2019-01-06 17:35:00, 2019-01-06 17:40:00]", range.last
+    assert_equal "2019-01-06T17:10:00Z", range.from.iso8601
+    assert_equal "2019-01-06T17:35:00Z", range.to.iso8601
+    assert_time_range "[2019-01-06T17:10:00Z, 2019-01-06T17:15:00Z]", range.first
+    assert_time_range "[2019-01-06T17:35:00Z, 2019-01-06T17:40:00Z]", range.last
     assert_equal 6, range.length
 
     range = TimeSlice.new("5m", from: "2019-01-06 17:10:00", to: "2019-01-06 17:10:05")
-    assert_equal "2019-01-06 17:10:00", range.from.to_fs(:db)
-    assert_equal "2019-01-06 17:10:00", range.to.to_fs(:db)
-    assert_time_range "[2019-01-06 17:10:00, 2019-01-06 17:15:00]", range.first
-    assert_time_range "[2019-01-06 17:10:00, 2019-01-06 17:15:00]", range.last
+    assert_equal "2019-01-06T17:10:00Z", range.from.iso8601
+    assert_equal "2019-01-06T17:10:00Z", range.to.iso8601
+    assert_time_range "[2019-01-06T17:10:00Z, 2019-01-06T17:15:00Z]", range.first
+    assert_time_range "[2019-01-06T17:10:00Z, 2019-01-06T17:15:00Z]", range.last
     assert_equal 1, range.length
   end
 
   it "accepts a :from and :length option" do
     range = TimeSlice.new("5m", from: "2019-01-06 17:10", length: 3)
-    assert_equal "2019-01-06 17:10:00", range.from.to_fs(:db)
-    assert_equal "2019-01-06 17:20:00", range.to.to_fs(:db)
-    assert_time_range "[2019-01-06 17:10:00, 2019-01-06 17:15:00]", range.first
-    assert_time_range "[2019-01-06 17:20:00, 2019-01-06 17:25:00]", range.last
+    assert_equal "2019-01-06T17:10:00Z", range.from.iso8601
+    assert_equal "2019-01-06T17:20:00Z", range.to.iso8601
+    assert_time_range "[2019-01-06T17:10:00Z, 2019-01-06T17:15:00Z]", range.first
+    assert_time_range "[2019-01-06T17:20:00Z, 2019-01-06T17:25:00Z]", range.last
     assert_equal 3, range.length
   end
 
@@ -90,11 +90,11 @@ class TimeSliceTest < TestCase
   it "gets previous times" do
     range = TimeSlice.new("5m", from: "2019-01-06 17:00", to: "2019-01-06 17:35")
     prev = range.previous("2019-01-06 17:20:00", 3)
-    assert_equal "2019-01-06 17:05:00", prev.from.to_fs(:db)
-    assert_equal "2019-01-06 17:15:00", prev.to.to_fs(:db)
-    assert_time_range "[2019-01-06 17:05:00, 2019-01-06 17:10:00]", prev[0]
-    assert_time_range "[2019-01-06 17:10:00, 2019-01-06 17:15:00]", prev[1]
-    assert_time_range "[2019-01-06 17:15:00, 2019-01-06 17:20:00]", prev[2]
+    assert_equal "2019-01-06T17:05:00Z", prev.from.iso8601
+    assert_equal "2019-01-06T17:15:00Z", prev.to.iso8601
+    assert_time_range "[2019-01-06T17:05:00Z, 2019-01-06T17:10:00Z]", prev[0]
+    assert_time_range "[2019-01-06T17:10:00Z, 2019-01-06T17:15:00Z]", prev[1]
+    assert_time_range "[2019-01-06T17:15:00Z, 2019-01-06T17:20:00Z]", prev[2]
     assert_equal 3, prev.length
   end
 
@@ -106,20 +106,20 @@ class TimeSliceTest < TestCase
   it "correctly handles different time periods" do
     range = TimeSlice.new("15m", from: "2019-01-06 12:00", to: "2019-01-06 13:00")
     assert_equal 5, range.length
-    assert_time_range "[2019-01-06 12:00:00, 2019-01-06 12:15:00]", range.first
-    assert_time_range "[2019-01-06 13:00:00, 2019-01-06 13:15:00]", range.last
+    assert_time_range "[2019-01-06T12:00:00Z, 2019-01-06T12:15:00Z]", range.first
+    assert_time_range "[2019-01-06T13:00:00Z, 2019-01-06T13:15:00Z]", range.last
 
     range = TimeSlice.new("1d", from: "2019-01-01", to: "2019-01-05")
     assert_equal 5, range.length
-    assert_time_range "[2019-01-01 00:00:00, 2019-01-02 00:00:00]", range.first
-    assert_time_range "[2019-01-05 00:00:00, 2019-01-06 00:00:00]", range.last
+    assert_time_range "[2019-01-01T00:00:00Z, 2019-01-02T00:00:00Z]", range.first
+    assert_time_range "[2019-01-05T00:00:00Z, 2019-01-06T00:00:00Z]", range.last
   end
 
   it "handles empty ranges" do
     range = TimeSlice.new("1h", from: "2019-01-06 12:00", to: "2019-01-06 12:00")
     assert_equal 1, range.length
-    assert_time_range "[2019-01-06 12:00:00, 2019-01-06 13:00:00]", range.first
-    assert_time_range "[2019-01-06 12:00:00, 2019-01-06 13:00:00]", range.last
+    assert_time_range "[2019-01-06T12:00:00Z, 2019-01-06T13:00:00Z]", range.first
+    assert_time_range "[2019-01-06T12:00:00Z, 2019-01-06T13:00:00Z]", range.last
   end
 
   it "correctly implements the Enumerable interface" do
@@ -153,11 +153,11 @@ class TimeSliceTest < TestCase
   it "correctly handles previous method with edge cases" do
     range = TimeSlice.new("1h", from: "2019-01-06 12:00", to: "2019-01-06 15:00")
     prev = range.previous("2019-01-06 13:00", 2)
-    assert_time_range "[2019-01-06 11:00:00, 2019-01-06 12:00:00]", prev.first
-    assert_time_range "[2019-01-06 12:00:00, 2019-01-06 13:00:00]", prev.last
+    assert_time_range "[2019-01-06T11:00:00Z, 2019-01-06T12:00:00Z]", prev.first
+    assert_time_range "[2019-01-06T12:00:00Z, 2019-01-06T13:00:00Z]", prev.last
 
     prev = range.previous("2019-01-06 12:00", 2)
-    assert_time_range "[2019-01-06 10:00:00, 2019-01-06 11:00:00]", prev.first
-    assert_time_range "[2019-01-06 11:00:00, 2019-01-06 12:00:00]", prev.last
+    assert_time_range "[2019-01-06T10:00:00Z, 2019-01-06T11:00:00Z]", prev.first
+    assert_time_range "[2019-01-06T11:00:00Z, 2019-01-06T12:00:00Z]", prev.last
   end
 end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index a89b69b..d764ac4 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,4 +1,5 @@
 require "minitest/autorun"
+require "minitest/focus"
 require "mocha/minitest"
 require_relative "../lib/time_slice"
 
@@ -13,7 +14,7 @@ def time_array_to_s(times)
     end
 
     times = times
-      .map { |times| times.map { |t| t.to_fs(:db) } }
+      .map { |times| times.map { |t| t.iso8601 } }
       .map { |times| "[#{times.join(", ")}]" }
       .join(", ")
 
diff --git a/time_slice.gemspec b/time_slice.gemspec
index 96037bc..03cea8d 100644
--- a/time_slice.gemspec
+++ b/time_slice.gemspec
@@ -15,13 +15,14 @@ Gem::Specification.new do |spec|
   spec.test_files     = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths  = ["lib"]
 
-  spec.required_ruby_version = ">= 2.7.0"
+  spec.required_ruby_version = ">= 3.0"
 
-  spec.add_dependency("activesupport", "> 5.1")
+  spec.add_dependency("activesupport", ">= 5.1")
   spec.add_dependency("rounding", "> 1.0")
 
   spec.add_development_dependency("appraisal", "~> 2.5.0")
   spec.add_development_dependency("minitest", "~> 5.24.1")
+  spec.add_development_dependency("minitest-focus", "~> 1.4")
   spec.add_development_dependency("mocha", "~> 2.4.0")
   spec.add_development_dependency("rake", "~> 13.2.1")
 end