Crossing the U.S border to Seattle?

hi , im going to seattle to go shopping at seattle premium outlets, then driving to seattle to stay a night, then maybe go shopping in alderwood, and when i cross the border, how much exemption, or something do i get ? does that make sense ? HAHA i checked the website and it said 24 hours you get 50 dollars, if i stay a night, is that considered 24 hours ? or 48 hours ? thanks ! :):)