It is much easier for time to pass unnoticed when you have music playing than when you have the television on. Especially if you're coding. When the TV is on, particularly if you use something like a TiVo to view your television, you are very aware of when each half hour or hour or two hour block of time has passed, since your show has just finished. Whereas it's quite simple for several songs to pass and you not realize it, it's all just faded into the background noise.
(This tidbit brought on by the fact that the last three hours passed without me noticing them.)