The Bayside at 5p.m. on the nose today, tax day.
If you're keen on using USPS, the Flushing location at 4165 Main Street is open until 8p.m. It's a good option perhaps if you're taking the LIRR from Manhattan, and can stop in Flushing on the way home.
, at 4206a Bell Blvd., is open until 7p.m., which are their regular hours.
There's also a FedEx drop-off location at the S, which is open until 7p.m.
FedEx has several other drop-off locations in the area, but those two locations are opened the latest.