What's the problem?
Glance at your watch on brakes off, takeoff, touchdown, brakes on and note them on the PLOG. What's difficult about that? And if your watch isn't accurate to within a minute, get a new one. Seriously.
How accurate do you make your position reports/estimates? If you cross the FIR boundary, do you tell London Info that you estimate the FIR boundary at around 10 o'clock? Crossing controlled airspace, do you call them and ask for zone transit, estimating zone boundary at around 20 past? No, I didn't think so.
Maybe I'm anally retentive, but I do expect to be able to record times to within a minute, and calculate ETAs to within a couple either way.
Tim