1000ft is total rubish.
You can start an auto at 100kts/50ft and be fully stabilised in time to make a landing, equally from 1000ft using minimum height loss technique you can be stabilised after about 50ft of descent if you are smooth.
Autorotation can be established almost instantaneously by pulling back the cyclic. This can be shown by the need to contain Nr.
If Nr rises by itself, then you are in auto.
Rate of descent is totally unimportant, only AoA relative to the disc matters.
There is absolutely no need for any descent to occur to be in auto.