Acclimated means a condition in which a flightcrew member has been in a theater for 72 hours or has been given at least 36 consecutive hours free from duty.
Theater means a geographical area in which the distance between the flightcrew member's flight duty period departure point and arrival point differs by no more than 60 degrees longitude.
If you are not Acclimated to Theater then your "Max Duty" must be reduced by 30 minutes. To make this adjustment, tap the figure under the "Max Duty" section and deactivate the "Acclimated to Theater" toggle. You will see the "Max Duty" value decreased by 30 minutes:
