Folks,
The law (as in LAW) is quite clear about what to log;
Blocks time (aircraft first moves under its own power etc) for the pilot log book.
Air time, wheels off to wheels on for the MR.
The Act/Regulations do not recognize any rules of thumb, as one major operator at YSBK (and owners with aircraft on line with said operator) found out to his/their very great expense, in a CASA audit.
The law requires you to have a timepiece in the aircraft, use it.
Tootle pip!!