Support for SOURCE_DATE_EPOCH was added in:

• Set SOURCE_DATE_EPOCH pack#1418
• Support SOURCE_DATE_EPOCH lifecycle#823

However, I only see it mentioned on this migration page:
https://buildpacks.io/docs/for-platform-operators/how-to/migrate/platform-api-0.8-0.9/#configurable-image-create-time

It should probably be added to:
https://buildpacks.io/docs/for-app-developers/concepts/reproducibility/

And maybe elsewhere? (Perhaps also the pack build --help entry for --creation-time?)