"Been there, done that!" - scanning and posting the article, I mean, on the instructor Forum a while ago.
Have a look (on the second page) at
Jacobson flare.
Personally, I look at the other pilot's face - when they flinch, it is time to flare!!
O.K. an oldie I know. Actually I don't like the term "flare" as it is a bit imprecise. I prefer "Round out" and "Hold off" - the round out being the bit where you transition from approach to landing, and the hold off being the bit you try to save your reputation as a gun driver.