In regard to when are you too low to be able to lower the collective/flare, I think the best way to think about it is to imagine a continuum from the hovering case (no collective lowering, no flare) up to the full -blown autorotation entry at height and with some decent forward speed (ie lower collective fully, flare to regain Nr and to get to best auto speed).
This is from AS350 experience, but it would be similar for most aircraft, in concept that is.
If you imagine transitioning from the hover into forward flight, it would go something like this:
hover - freeze collective, no flare.
taxi - as above
up the slope a bit - partial collective lowering, small flare (as much as you can for both without digging the tail into the ground)... and so on.
In the Squirrel, you can get a softish landing (albeit with some run-on speed) from anywhere up the slope from the hover to a 60kt/100 ft AGL gate (height figure may be wrong, it's been a while!).
The judgement part is getting the feel for how much flare and lever-lowering you can do before you have to give it away and adopt a skids-level (or maybe a tad nose up) for the run-on.
So (finally), in partial answer to your question I hope, you should be able to get a bit of lever down and flare effect anywhere from about 10 or 15 kts on takeoff.
Hope I haven't dribbled on about stuff you weren't looking for.