The original Veyron could change gears in 8ms, and will, IIRC hit 60 in 2nd. Changing gear isn't going to be a considerable part of the time here.
Wikipedia https://en.wikipedia.org/wiki/Bugatti_Veyron states that the original Veyron gearbox could change gears in 150ms, so it is a considerable part of the time.
While the gear are shifting the engine RPM must go down then up; the 8ms figure certainly doesn't account for the complete sequence.
See https://www.quora.com/Why-don%E2%80%99t-Tesla-cars-need-a-ge...