git commit --amend --date="Wed Feb 16 14:00 2011 +0100" --no-edit
Certain proponents of Fossil and Mercurial will tell you that this is an advantage of those systems - They're fooling themselves, because you can make those edits, there's just not nice tooling for them.
So I guess it works in my favor because I own the git repo.
There's always something, isn't it. I can change my git timestamps and the employer can change its server log timestamps if there's maleficence at either side. That's a completely different territory then.