I applied for my parents last April..It took me almost 3 Month after getting the receipt number...I was also familier of the case which was done within 3-4 weeks its really depends. As of now I really think it will take 3-5 month..Yeah you can leave the country after the finger print but USCIS people wants you to wait at list 2-3 weeks coz sometimes finger print doesn't go through and you have to redo finger print.