The mailman does not usually deliver parcels on Saturdays (or Sundays) but since the post office is open on Saturdays, is there any difference between posting an item on a Saturday and posting on the following Monday?

When I post an item on a Saturday, does anything happen to the parcels? For example, do the contracters/van drivers pick up the parcels on the same day? If this is the case, what's the supply chain process? Do they make productive use of the Saturday/Sunday (eg. parcels during the weekend go by car/plane instead of staying stationary)?

Or do my parcels sit in the basket/storage for the rest of the weekend until it gets picked up on Monday (so in this case, there is no difference between posting an item on a Saturday and a Monday)? In this case, I might as well stay home and enjoy my Saturday.

Also, do the weekend parcel activities (if any) depend on the Post Office branch?