a friend asked me to find out
You don't have to go to college to get to the pros. There is no set amount of time though, time on college is time to play, get better, and get noticed. Could be 6 months, could be after graduation.
There certainly is a set amount of time.
You need to do your own research. Search for "NFL draft eligibility" and see what you find.http://en.wikipedia.org/wiki/NFL_draft#Eligibility