This is being http://www.gamesas.com/topic/1522326-is-this-a-game-you-constantly-have-to-tend/ as well.
You can be rather casual or a power player, it's up to you. As long as you return to the main menu before closing the app or locking your device. I have been going to the small gears icon for the http://i.imgur.com/LfujnTF.jpg. On that menu is an option to go to the http://i.imgur.com/hYOTQSp.jpg. Go to the Main Menu before closing the app or locking your Phone or Tablet.