Duo Offline Codes - How long are they valid for?

Hello,
I cannot seem to find documentation on how long offline codes are valid for.

Scenario: I have a user that will be traveling to a remote area without cellular service and no internet connectivity and has completed offline enrollment for his laptop.

How can I be sure his offline codes will actually work? I tested myself by turning on airplane mode on both my cell phone and laptop, let the offline code change a few times and logged in just fine… but what he’s without both cell and internet for a few days?

As noted in step 4 here, the maximum offline duration may be set for up to 365 days (so the user will be able to generate offline passcodes and log in for the duration you specify). For a test I’d suggest what you already did.

With that said, offline access is intended for temporary offline use, and not intended as a permanent offline solution.