cd path/to/git/project
export GIT_COMMITTER_DATE="YYYY-MM-DD HH:MM:SS"
export GIT_AUTHOR_DATE="YYYY-MM-DD HH:MM:SS"
git commit --amend --date=""YYYY-MM-DD HH:MM:SS"
# Verify date and time then save.
unset GIT_COMMITTER_DATE
unset GIT_AUTHOR_DATE