For me the reset is 0000GMT, but the seasonals are updated at 0400. I'm guessing a tweak like this would come with the seasonals rather than the trade reset, as that seems to make more sense.
It would be strange if they didn't synchronise the reinstatement of the cap, though, so maybe it'll be reinstated at midnight in Japan or Australia? Or maybe it'll be midnight in the US instead? Who knows, PD have been known to be strange in the past...