The maths is quite easy. If doing ~700kts (M1.0) then that's 10nm/minute, so 12 minutes. At ~1400kts (M2.0) then that's 20nm/minute so 6 minutes.
Apparently your maths isn't up to scratch...!!
10nm/min is 600kts g/s. Speed of sound at sea level is ~660kts, so 11nm/min.
Close enough!
A bit like the supersonic RNZAF Strikemaster that had broken windows and cracked a house wall. More proof that the Blunty could defy the laws of fluid dynamics.