Ex-profile tool?It seems like only Microsoft has an insight on this.
If i were you, i would never put a timestamp on an achievements and unlock it online. I highly advise you to unlock them offline instead. If people file a complaint on your account, MS could see if you were online at the time when you apparently unlocked the achievement. So just go for the Singleplayer Achievos and do the online ones yourself to get not caught.
Btw. if you are using Profile Tool 2.5, Horizon or Le Fluffie, give them up. They are not getting updatet and thus are very buggy and can lead to a ban at the worst case. http://www.djekldev.co.uk/v3n3/exPE/Site/ This Gamerscore Modding Tool is the best atm.
Also read this http://www.se7ensins.com/forums/topic/269217-modding-your-gamerscore-want-to-look-less-suspicious/ to lower the risks.