Based on an amateur use of mtl, I think it's supposed to say it used 6% of his MP, so being worried about using 6% MP in 2 seconds when his regen is 1% per second is valid.
@lumberhoss Thanks for double-checking with the raws. 6% in two seconds is still a pretty good rate, considering that it significantly slows his perceived time-rate, and can be used a third of the time indefinitely without cutting into his other magic use. Two seconds of super-speed with four seconds of (still pretty quick) regular speed is a great deal.