I don’t know what they would have flown but i assume the military rapid response is going to be at least as fast as the most common passenger jet.
“The 747-400, the most common passenger version in service, has a high-subsonic cruise speed of Mach 0.85–0.855 (up to 570 mph or 920 km/h) with an intercontinental range of 7,260 nautical miles (8,350 mi or 13,450 km).”
Something in the neighborhood of an hour then, since theres takeoff to consider, and they would have been landing. Ninety minutes from when that email was received and they could have been on site. I’ll assume the killers would have been informed by their allies of approaching US forces so they may have simply broken off the attack at that time. I don’t know if Stevens was already dead at that point but it adds to the likelihood of saving the the others since he was the target.
Where was the nearest carrier? I bet a couple determined Marine F-18s inbound at mach 1 plus might ruin that crowd’s day if they stuck around.