It'd depend. First, on the school and the time it will take to issue an I-20 (what it issues after you've been admitted and all your documents are in order). Then, on the embassy/consulate to schedule you an interview, process your application and issue the visa. There might also be other facts that might delay the process, such as being from a state-sponsor of terrorism, et cetera.
I recommend starting the process several months in advance to be on the safe side.
For further research, contact each individual school you are interested in for their local process and processing times, and then contact your local U.S. embassy/consulate to find out their processing times.