Let me get this straight, this store only cleans its restrooms 3 days a week. Who does the clean up the other 4 days of the week ???
Why a day shift for clean up, seems more logical to clean the freezers, floors, bathrooms at night, no customers to try to work around.
I did clean-up a couple of years ago for a convenience store - two nights a week midnight to six for a couple of months until the manager could find a permanent person (I had been going to that convenience store for daily coffee since about 1995, so the mgr asked me to fill in)
One morning the mgr asked me how I could be through at 6 when the second cashier (there was only one on my two nights) would have to stay until 8 to finish.
The answer was - come to work at midnight, start, don't stop until it's done. Easy peasy.
And no, I didn't want the job permanently.