put the actual time you're on IMC?
I think you might be better off concentrating on flying the aeroplane, rather than trying to record the time of every entry and exit from cloud!
If anything, I think the correct answer is as Mr Bernoulli says. That said, I'm not aware of many airline pilots who put anything on the right page of the book. If your flying an airliner, every flight will be IFR so who really cares about any time other than your total time.