How long does college take to become a music producer?

Two - four years.

An associates degree is a 2-year proposition but most employees want a 4-year degree which is called a bachelor's degree. Here's some other info I found by googling:
Ok first off, you need to know the different between a producer and a person who makes beats and creates hip hop songs for artists. A producer's ONLY job in the studio is to be the director in the studio, telling others what to do, and managing the time and money. You are like the director of a film. So, do you want to be a composer or a producer? If you don't believe me because people in hip-hop call themselves producers, please google it before you start saying you are one, or other producers WILL laugh at you.

Anyways, sorry for the upfront attitude. But here is how you become a credible producer.

You frankly just work with a few people you know who make music and produce them for free, or you can go to an audio engineer school, via financial aid.

You make money by royalties negotiated in a contract, and you receive back end money from any use of the master recording unless you work under a label. You make money by charging someone insane amounts, Labels hire people to produce records for 10-150k, just in two months. NOT beat makers, but actual A-Game producers.

Bottom line, FIND a friend who has gear and learn from him what it takes to record a band or group, youtube it, google it, go to gearslutz.com.