When does the 29th start?

Simple question really. There's a message in-games saying that "double drops" (whatever that's defined as) on August 29th. When does the game define the start of August 29th? Other games I have played used 00:00 GMT, or 00:00 PST, but I haven't been able find anything saying what this game uses. It would be really helpful to know when this "double drops" thing is actually in effect.