Thanks a lot, 40hz.
I looked up the EventLog, but I admit I was not yet able to find out which EventID numbers are for the named power states.
Perhaps you can consider to give more information later, my question is not urgent. I suppose all the needed information is in the EventLog, but I did not find a program to read it easily. "PC On/Off Time" does not work correct, else it would have been satisfying for my purpose. I would like to distinguish between "off", meaning S1, S2, S3, S4, S5 and "on".
Result given as list, e.g.
and so on