OK well 4 hours is probably an exaggeration but I know I waited approx 90 minutes, approx 2.5 hours from the moment I began standing in the ticket line and actually had the tickets in my hand. Note you don't actually receive the tickets but a voucher that you must redeem at the box office. IIRC you can't wait till just an hour before the show to redeem it either. The tickets that I ended up purchasing, while they were nice seats, were not ones I would have purchased at full price so it resulted in virtually no discount from my wallet's perspective.

Look out for deals every week--I'm sure there will be some 25% off deal somewhere when your trip is closer. There are holiday promotional tickets on the mirage website but unfortunately those end at the end of March.