As far as I know,
DAS does not operate at MHP. And you're right about most of the lines being fairly short -- I've never had to ask for a return time at a party. But DAS should work during the party's early entry hours.
I disagree about this. On the surface, Disney customer service can appear to be a monolith of strict rules and regulations. And, of course, any large company can have their fair share of bad apple CS employees (and that includes all the airlines, too). But once you pursue your case further with Disney, there are CMs behind the scenes who are very willing to take the time to work with you one on one to find a workable solution to your problem. We've had some very compassionate CMs work with us to the point of back and forth phone calls over a week, personal letters, refunds on non-refundable tickets, and follow up phone calls (which were not obligatory or mandatory in any way) to find out how we were doing. I would like to think that Disney customer service would be much more open on the surface if Disney as a company weren't such a target for so many scams and frauds.