3 months as per most school's advisor.
School advisor can help you in this matter

hey Stewi, I am in the same situation. I just did my fast processing a week ago so that i will have my decision by next week.......When i talk to advisor we have 60 days to issue I-20 and anoother 3 moinths to stat collgege............can u please tell ur frd to contact me.........

Hi
if you wish to join in a school, a school in california here you have an opportunity i.e you can take your cpt from the beginning sem and can choose online courses,no need to attend the school.
for further details mail me on hvenkatesh1@gmail.com