Music, draw, animations must be in the 3 hours? 

I think they must be stitched together, not necessary create the assets in this period. "D

« The time for coming up with an idea, making a design doc, compiling the game, publishing it, etc. does not count in the 3 hours you have, that time is purely for development of the product. »

That’s on the page of the trijam

I would say, yes, the development counts the code, the visual and the audio.

That’s how I calculated my time.

I think you can do the music before, but you should do the animations and art during the 3 hours.

"On using pre-made assets: make sure you have the necessary rights to the assets you use in your game." this is in page too.