i actually waited a day. the whole point of this exercise for me was to be able to quickly and cheaply get the car looking nice & clean on my own schedule. it took a lot of elbow grease because of pre-existing stains that had been on the paint for a long ass time. now that they're cleared the next time i wipe it down should be cake.
the cost of the wash was $10 bucks. the cost of the spray was around $15 with 3-5 uses per bottle (so i use sparingly at $3 per detail). total cost per exterior "wash" is $13 for me. i figure i'll do it twice a month. i hear there are higher-end spray detailers but i'm more for convenience so whatever walmart had was good enough!