They address this in the FAQ:
We have a mail drop in the Airport Authority offices, which are open during regular business hours (Monday through Friday, 8:00 a.m.–5:00 p.m.).
Note the times it’s available: Monday-Friday, 8-5.
The Airport Authority office is on the terminal map. They’re on the second floor by the conference rooms; this is probably pre-security, but the maps are indifferent to where the secure zone is for that floor.
Robert was able to verify this. Thanks Robert!
Last Updated 23 November 2021