In the civil world, for the portion of the H-V curve that is above the knee (i.e. youre in level flight), a one second delay is used from time of engine failure until the collective can be lowered. The cyclic and pedals can be moved immediately (the logic is that you might not have your hand on the collective, but it would be extremely unlikely that your right hand would be away from the cyclic, or feet off the pedals). From the low hover point to the knee, there is no intervention time, based that you should have your left hand on the collective - but also note that takeoff power is used for this portion.
For the military, a two second intervention is used for all controls. A life time!!!