There's no point getting too scientific about it... although rate 1 (or .5) the only NCNG turns I would bother to time would be long turns i.e. more than 90 degrees (as much for workload management, and so I didn't forget the guy was in the turn, as anything else)... any smaller turn was done by "grabbing a handful" - a bit of experience mated with trial and error seemed to work? (with fast traffic it is easier to watch the turn on radar, slow traffic wouldn't go too far in the wrong direction before you notice).