The rotation is every other trip as far as I can tell on those types of shops. It seems the office supply are every other trip, and the grocery are 2 out of 3 trips. Or at least that seems to be the rotation in my area. I did an office shop about 3 weeks ago, tried again this week and I'm in violation. If no one picks it up, or it sits, etc. you'll still be in violation. That being said, you can always write to them and see if they can break the rotation if it sits too long.