Sometimes you just gotta fix a date in git commits, and this can happen for a wide variety of reasons. Maybe you were on a system with an unset clock and you want accurate timekeeping, maybe you don't want to admit you were up at 4AM coding. I get it. Here's the fix:
git filter-branch --env-filter \ 'if [ $GIT_COMMIT = 119f9ecf58069b265ab22f1f97d2b648faf932e0 ]; then export GIT_AUTHOR_DATE="Fri Jan 2 21:38:53 2009 -0800" export GIT_COMMITTER_DATE="Sat May 19 01:01:01 2007 -0700" fi'