dublinpilot
I don't think there is a universal answer to your question because in different planes the readout you refer to can mean different things.
It can be a straight RPM count, running all the time the engine is running. It can be a timer activated by oil pressure, landing gear up, or even airspeed. It can be a straight engine-running-time timer which ignores RPM (that's what I have).
It doesn't really matter (because one logs the actual times anyway) unless you are being charged on the basis of the reading, in which case it's possibly a ripoff.