Scratch

I'm sure it varys depending on the command you give and the data you ask it to do it on.  Doing a Whirl command on a full screen sprite takes longer then doing it on a very small sprite, for instance.  Also, the speed of your computer will make a difference too.

If you're using a bpm interval, you might want to take the global tempo-blocks (from the sound category) to set and get it. You can then use the rest-block (also from the sound category), which takes a bpm-value, instead of the wait blocks.

Synchronizing music with other threads in Scratch is a nice challenge. It usually involves cutting up long recordings into shorter "sound bites", and synchronizing them using broadcasts. (also check http://scratch.mit.edu/forums/viewtopic.php?id=8616 )