Having worked at one of the big banks, I see why you might ask this. But, having moved out of the big bank world I now close loans in weeks, not months! How refreshing, right?
I recently closed an out-of-state purchase deal that needed a mail-away closing in 13 days. And that was with the borrower having trouble producing necessary documents. As someone mentioned, that is atypical in how we'd prefer to do things, but know it is possible. I typically say upfront that 3 to 4 weeks gives us plenty of time. At my company, if I have already pre-approved the borrower that is usaully plenty of time as we do more upfront to qualify borrowers (which equals less time once they find a property!)
With purchases there are so many variables- from the borrower's situation and ability to provide documentation, to the appraisal, to title work. That's when having a loan officer who can guide the transaction through thick and thin and communicate effectively to all parties involved becomes so valuable. If you find yourself wanting to work with someone like that, I am always available.