Visited on May 15 and did a short charge with M-CHARGE RFID. No issue.
Based on the satellite and street view images, I thought the parking was like the secondary parking at Migros Rheinfelden, where it's a bit further away and you then have to walk to the store. But in fact it's a massive ramp that goes all the way under the store.
The chargers are in Level -1, the first level at the bottom of the ramp. There are no EV signs at the fork between -1 and -2, but you might be able to spot the chargers or the M-CHARGE arrow further down in the lane.
There are big gates at the parking entrance that could be used to close it for the night, but in the Migrol app it's indicated 24/7 and I didn't find any posted closing time for the parking. There are other businesses including the wellness center which is definitely open on Sunday.
In the parking I didn't see any parking meter, time limit or any other instruction apart from the generic ban sign for customers.
I didn't spot where the night exit might be though. The only stairs and elevators I saw lead to the Migros lobby. I assume this area remains open on Sunday because it's also where the main entrance for the other businesses is.