You can always commit using:
GIT_AUTHOR_DATE="Wed Sep 24 14:12:30 2020 +0530" GIT_COMMITTER_DATE="Wed Sep 24 14:12:30 2020 +0530" git commit -m "message"
Been using this trick for years to show clients that the work is consistent over a span of days when in reality I’d build it in the first day or so.
Also, the amend one is fine if the commit is an unpushed commit (repo is local-only still).