You can tell a lot about how centrally located a place is by how late FedEx and other parcel services do pickups. Here's a directory of where you can do a late drop-off.

Official site: http://fedex.com/us/pckgenvlp/ship/

The latest drop in the city is FedEx Express Ship Center, 4556 Concourse Dr, Ann Arbor, MI 48108, which is staffed until 8pm and has express dropoff until 8:30pm.