Latex balloons in a box for reveal helps

Ok we are doing our gende reveal today with balloons in a box. We have 1 big foil balloon and then we will blow up latex balloons around the foil balloon. We will be doing the latex balloons at 11:00-11:30 putting it in s box then doing the reveal. Does anybody know if the latex balloons will last? The party store said 7 hours.