If you use the OpenSprinkler mobile app, then you can still access the controller without Internet. The only reason it needs Internet is to perform NTP time sync and get weather data, but those do not prevent the controller from running programs since all program settings are stored locally on the controller. When you use a browser to access the controller, it needs to access UI files (javascript files) stored on the OpenSprinkler server, but if you use the mobile app, it already embeds these javascripts so it won’t even need to access the Internet.