What do you hope/expect "Shipped" to mean? Just package prepared, or in the hands of USPS?
I know there are some vendors for whom marked shipped simply means shipping label created but not getting sent until tomorrow where as for others it means the package is in postal control.
Thoughts?
First move is to read the vendors profile and see when they ship. If they DO NOT mention when they ship, I assume it is weekdays only. If the order is marked shipped during the week, I assume it is out of the vendors control. Put in a blue box, whatever. That DOES NOT automatically mean that USPS has it.
If the order is marked shipped on the weekend, I assume the package will go out on monday.