The post office has been great!
I had two different shipping times for them.
The first was 40 boxes (pre-addressed and stamped)
The second was for 42 boxes (38 pre-addressed and stamped, 4 had to go through the paperwork, weigh-in and stamping for international)
The first shipment took all of 15 minutes (They let me borrow a mail trolley)
The second took about an hour due to the international (not that I minded -- but the postal clerk was not really in a hurry that day! LOL)
Kurt