As a member of an ARA (Aerial Rocket Artillery)unit in Vietnam, I'd like to respond to your question. From the time we received a call for a fire mission we were to be airborne in two minutes. So let's carry that through. Probably at least two minutes for the radio message from the grunt unit to reach our operations, two minutes for us to get in the air, anywhere from 2 minutes up flight time to target, and probably another minute or two marking target, orientation, before the rounds really start to impact. And we were considered quick response....
So, a 2 minute delay for 105 support actually seems pretty speedy. And this all assumes no competition from other missions.