Leading into the performance with advance sales, selling at the event and a couple weeks between the event, delivery of a final product and initial order cutoff is pretty much, as you've experienced, all you are going to get. But, that figure could be high, or good enough, depending. (actually I NEVER have a cut off date and have over the years received numerous orders for previous productions due to loss, damage, belated relative requests, etc.)
A typical two-hour, or less, performance for us takes about 3.5 hours in acquisition, less than 6 hours editing, less than 3 hours setting up the DVD & chapters, less than 2.5 hours for duplication and packaging - 15 hours or so. Production shouldn't take much longer than that, on average.
Yes many dance recitals can hit the 3-hour mark, or in your case and some of mine, there are multiple shows with different dancers/dances on different days. We have produced a weekend recital gig with a Friday evening performance, three performances on Saturday, a Sunday matinee and Sunday evening performance. Whew. It is a different ball of wax and the logistics of such productions can be overwhelming, depending on the school/client expectations regarding production value, cost of services and total numbers of sales (including the inevitable "My daughter/son is in four performances, can I get a deal?") Flexibility is key in both working with these people, some really serious primadonnas are to be found in pretty much any performance event, and in developing pricing that works without feeling like you were totally screwed.
 Never promise more than you know you can deliver, or ask for more than you think your client studio is reasonably willing to invest - in time, cooperation, effort or money.
Orders will "fall off" a couple weeks after the event - some due to bootlegging between friends, but mostly due to the fact that other events, family activities and life in general begin shifting your production video to the bottom of the "gotta have it" pile. Much of event video production sales success is in the "impulse aisle" or "emotion of the moment" category and that diminishes rapidly with time.
I try to not EVER deliver ANYTHING until either the minimum sales has been met, or before that magical two-weeks after the event period, knowing that early delivery of copies will tempt the bootleggers. Keeping within this timeframe will usually generate the highest potential level of solid sales.
