In my experience in the past, if the Guidelines say that you should wait at least 20 minutes before leaving, be sure to wait at least 25 minutes and take a photo of the store with the time, date, and GPS location on it from the parking lot. If it doesn't say that you can leave after 20 (or whatever minutes), you won't get paid if you leave. I have on occasion left and then returned later when I thought that the store would be less busy. I also stopped accepting shops with that scenario.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008