Lots of good advice here.
Knowing the control response when you're close to the ground is key -- not too much, not too little.
With some people I would take them up the TV antenna mast so they would see the height where they could make out individual stems of grass.
When you can distinguish surface texture is the time to flare.
We're talking about 3-5 seconds in ground effect with the inevitable crosswind while making fine adjustments to pitch, bank and yaw. A very efficient circuit would be some 6 minutes; so, there's barely 1% of the flight in the flare regime.
15 landings gives you just 1 minute's experience of the flare.
It's going to take 900 to get an hour's worth
So yes, the advice to find a long runway and flying just above it could speed up the learning considerably.