App access tokens tend to “wander” somewhere between 55 and 65 ish
Similar to implcit users tokens.
The documentation doesn’t state what the duration will be. So probably.
The example in the docs says 3600 which it naturally isn’t 
So best bet is to honor the response from the Token Generation API and/or whatever the Validate Endpoint reports when testing a token.
Personally I tend to test my App Access tokens every hour or so (on a CronJob) and auto regenerate them if they have less than a day ish left.
So if the duration changes my code doesn’t care as it’ll just regenerated when theres not much time left on the active token.
Just a reminder these are for “Server to Server requests”. And shouldn’t be used in client facing code.