You can call the customer service line and ask; as a rule, it will not be checked in and received for any kind of action today; and in some cases, the PO does not permit pick up on a standard delivery item as it means finding it and pulling it from their regular deliver run.
It is likely on a pallet with hundreds of other packages that won't been sorted by the clerks at your local P.O. until early tomorrow morning.
Call the post office first. Maybe the package is already loaded on to the mailman's vehicle.
You think you would be able to, but no. They won't let you.
No.
