429 status response -- Should the server specify an amount of time for client to backoff?

[LisoUseInAIKyrios]

A http response code of 429 means the client should backoff on making calls. But how long should it back off? The amount of time is not defined.

Should the server itself specify how long the client should backoff?

In the 429 response, should the http body include the number of seconds the client should backoff? It would be useful to more gracefully handle the level of demand on the server.