Decided to spend some time studying behavioural pattern of cluster/receiver
I measured voltage on receiver inputs and was surprised there is nothing there -- cluster doesn't keep receiver under power all the time. So I connected a LED (basically a bulb) to receiver power inputs and waited a bit. Nothing happened
Then I drove car and when I switched off ignition and removed key after the trip the LED immediately came ON (but only for about 5-10 minutes, I didn't measure exact length).
Interestingly, if you just switch engine on/off when car is stationary and remove key, this will never happen. Cluster should receive a bit of speed signal when ignition was ON. Only in this case the receiver gets power from cluster for 5-10 minutes when ignition goes OFF.
Taking into account signal structure (it takes one full minute to receive time and date signal) there are only 5-10 attempts to read time from air until cluster shuts down the receiver.
Perhaps receiver is switched ON at random time periods when car is parked. I will learn about it soon.
UPDATE: Receiver is always OFF while driving. If receiver was ON after accomplished trip and then I decide to continue journey, the receiver will go OFF immediately when I switch on ignition.