Have Quick 2,
The RAF Germany Battle Flight HASs for Phantom FGR2 / F-4M were equipped with INAS heaters. RS05 was held 24/7/365 with crewroom to airborne times in the region of 2.5 to 3 minutes regularly achieved, particularly during TACEVALs. During a forward deployment trial to use the ex-Lightning QRA facility at RAF Gutersloh in 1979, I once recorded a crewroom to airborne time of 1 min 40 sec when INAS alignment was dispensed with and the taxy distance to the runway was slightly less than that at RAF Wildenrath. So fast enough !