Well, Thursday midnight shows are technically on Friday.
And didn't it only beat Harry Potter's OW by like 5 million? Iron Man 3 made over 15 million from Thursday evening shows which started at 9 (although I know my theater, for example, didn't even follow that rule and actually started shows at 8). They were able to get a whole lot of shows in at various times before midnight. I don't think it's fair that studios are folding in what's basically an extra half day into the Friday estimates.