How soon can you get on-base housing?

I know it depends, but how long should I expect to wait for family housing on base after my husband is stationed? My husband should be finishing basic and AIT when I'm 33 weeks pregnant, and I'm not thinking I'll want to move too close to my due date, or soon after giving birth. We're thinking I should just stay with my parents until housing is available and I'm ready to move, but how long will that be? Is it possible that housing will be available immediately upon finishing training?