i doubt id waste much fuel, id rather look after the motor than have it operating under load when its stone cold..
Im never in a rush with my engine cold, why is there so much concern over a short idle time, are you that short of a dollar? The issue is not wasting a dollar here or there on fuel , its the longevity of the motor. After spending a few thousand dollars on a brand new turbo, im not going to take off at the turn of a key.
My brother did that in his rotary he had and it blew some seals somwhere, turnt into a smoker.. so in that case it did need warm up time.
i take 5mins just to get out the front gate, theres a notable difference after 5mins, the motor is free'd up a bit rather than cold and groggy..