Around 2-3 months I think & mine was rushed as the pre-production stage went waaay overtime. It helps a lot if you have professionals working with you. You need to consider the following things for post-pro:
I may have forgotten something =/ I didn't have any but it's also the time you do stuff like multimedia aspects & special effects but as I didn't use any of that, so I can't tell you anything about those areas.
Well i do have a professional in editing in general, but predominantly within the whole music and sound department. I am, as of now, researching a lot of music tracks from other soundtracks of films and hoping i might be able to incorporate those in my film? Is that legal? I'll do a search in a sec..
But anyway, Hmm 2-3 months is feasible, i plan to leave perhaps even more then that since i am beginning my planning/pre-production phase now.