It would perhaps be an advantage to be informed on the Internet or wherever that parcels can only be collected until 7.00 pm. Regardless of whether the store is open longer.
I haven't found any such information at https://www.migros.ch/de/services/pickmup.html; there's nothing like that under FAQs either. I actually always thought that you could collect parcels from PickMup for as long as the store where you had the parcel sent was open. Perhaps Migros can shed some light on this.