[v3.3] FIX: Short interruption between two continuous heating hours is eliminated.

In the case of two consecutive heating hours, Shelly used to flip between them with a 1-second gap because the timer was set exactly to 3600 seconds.
To prevent a brief interruption between these heating hours, now 2 seconds added to the Shelly timer.
The new default timer is 3602 seconds. This adjustment ensures that when a new heating hour begins, the countdown timer resets smoothly without causing any short interruption.