Internet access is required for the purchase of a policy, but not for the use of a policy.
If you know that you will be in an area without internet access, you can prebook your coverage ahead of time. Just open the options menu, select the “Prebook” option in the Schedule section, and select the start time/date. Then locate your takeoff point by panning the map or using the search function and searching for the address. Purchase as usual and your coverage will begin at the time you chose automatically.