Git: reset commit date

To reset the last commit date (both author and committer dates, which are the same within a local repo):

git commit --amend --no-edit --reset-author

To do the same for others than the last commit, rebase instead. To reset last 3 commit dates:

git rebase -i HEAD~3

For all commits, select e (edit) command instead of default pick, and amend them as described above:

git commit --amend --no-edit --reset-author
git rebase --continue

Check that the dates have been properly reset:

git log --format=fuller