I'm on page 44 right now but replying anyways to this pointless Harry Potter vs AoU previews/midnights debate.
Your comparing the wrong elements. It's not the hours that matter, it's the amount of screenings.
Last night, my local megaplex with 23 screens had 11 AoU showings from 7pm to close. Two of those were after midnight showings.
For Deathly Hollows II, they had 23 showings, on all 23 of their screens, at midnight, and many theaters did the same thing, locally, and nationwide. The demand for those midnights were much higher than the AoU previews due to the "finale factor" of the franchise that many people tend to ignore.
You also cant compare a preview nigt in APRIL (technically) to one in the middle of July.
AoU and DHII are completely different beasts. Stop comparing them.