Patrol is the 'idle' feature of King's Bounty: Legends. One can send their army on patrol for 1, 3, 5, 10 or 20 hours. Only 1 & 3 hour patrols are freely available though. To use the other periods one has to use a Ranger's License, which can be crafted or sometimes as a reward from treasure chests. As your level increases you will be able to make the ranger's and cammanders license from the items you get during battles. The Commander's License doubles the rewards from a patrol.
On patrol the army randomly encounters gold chests, treasure chests & battles. The level of the enemy army is according to the location the patrol was started from as well as player level. Battles reward gold, XP, or (mortal) units. If you finish your patrol, you get an extra sum of gold.
If you interrupt your patrol, you get the gold, XP and chests you've accumulated so far. But you miss out on the final gold reward. You will be locked out of going into another patrol for 10 minutes at the completion or cancelation of a patrol.