John,
At high altitude, similar to a Vigilant, about an hour to 251 knots! Only kidding!
On the deck, say 1000' amsl, acceleration in full reheat from 250 kts to Vne of 750kts would take less than 30 secs. The aircraft would still be accelerating and would not brick wall until approaching 900 kts. The acceleration is impressive but when the burners are pulled out the decelleration is even fiercer.
At high altitude the jet accelerates relatively slowly from 250kts indicated until the intake ramps start to work at about 1.2 mach but then, if clean, will accelerate nicely until the fuel runs out or mach 2+ is reached.
The crews main consideration in these circumstances, beyond getting the shot, is how fast the fuel disappears over the side.
Hope that helps,
Ghost
