Hmm... My alarm clock is 5-10 mins fast... I think that it runs just a bit faster then "normal" time, but i'm too lazy to figure out the correct time so i leave it at the wrong (fast) time.... Then again the main clocks that I use in my house are always off (vcr clocks). If I really want an "accurate" time, I usually go by my cell phone tho
When I do know how fast my alarm clock is, I do the math to get the correct time, and if needed I will use the extra time to prepare myself to get out of bed.