Dont worry about the 24 hours, whenever, however you file it just put the previous or same days date on it as my landlord always does. 3 weeks after I arrived last time.
But Brandon, that contradicts your very first reply to my question: "Normally when you receive your extension stamp in your passport is when they also staple a piece of paper telling you when your next(first) 90 day report is, which should be 90 days from when you receive the extension. "