Does how much you physically rewind  actually affect how much the song is rewinded?
 
 
For me I play on hard/expert and i spin the record only 1 revolution for my rewinds.
 
But when my friends played on medium, they rewind it 2-4 full revolutions and the song goes back a good 10-15 seconds
 
Is it the difficulty, how much you rewind physically, song choice, or just the timing of the rewinding that affects how much of the song is rewinded?

I think I understand your question, but your sentences are a bit confusing. 
 
I don't have the game anyway, but I think not many people will understand your question so quickly.

reworded it a little bit... that somewhat better?
 
If you cant tell, my english is bad lol

I've heard, and it seems pretty true from my experience, that THE MORE DIFFICULT THE SECTION JUST COMPLETED, THE FARTHER BACK THE REWIND GOES 
 
So if for example, you use a rewind during the crazy part on herbie hancock (expert), it'll rewind a long time, as opposed to just after a couple taps.