Why should you worry. If they like you and you drug tests come back clean then you should be fine. Unless you do drugs then you should worry.
24-48 hours
Well, I can’t speak for Wal-Mart specifically but here’s some good ideas:
Did you pee in a cup at the store? Those tests have immediate results. Did you go to a lab? They usually know within 24 hours. Either test may need further analysis… add 2 more days onto your wait if so.