How do they know when it is going to happen?
Waiting and have the required patience, perhaps? And ensure a healthy supply of extra power being ready all the time.
They might have warmed up (intentional pun) by watching one of the "slow TV" transmissions so popular in my country. For example: Showing 'A fire blazing in the fire place', 'Taking the train from Oslo to Bergen', or 'Going by coastal liner along the Norwegian coast' - literally - minute by minute. An entire TV channel was allocated for those broadcasts. You'd turn on the TV and followed until you fell asleep - when you eventually woke up, the program still was on