> I think you do this better with filter-branch too. But I don't know that command as much.

It goes like this:

   git filter-branch --env-filter \
       'if [ $GIT_COMMIT=186ba2fd6bca97c901194d9450c694c2836064d2 ]
         then
            export GIT_AUTHOR_DATE="Fri Apr 11 21:38:53 2014 -0800"
            export GIT_COMMITTER_DATE="Sat Apr 12 01:01:01 2014 -0700"
        fi'