"it depends" on the length of the drop (if any) placement of the knot , etc...

Done well, the insult to the cns from having the neck broken should hopefully cause near immediate unconsciousness

Failing that, compression of the arteries supplying blood to the brain should do it within 10 seconds or so.

The cause of death is still usually strangulation though. So there can well be a lot of suffering if any of the above don't lead to rapid loss of consciousness.