In 0.9.3 (and in some previous versions), there is a minimum nitro spending time.

As the bonus keeps going for a time after the key press stop, and as it has a fade-out time, it's better to use it in bursts as short as possible.

But is it good to only press the key very fast ?

No !

There is a bug which does that even if nitro is consumed, it won't have any effect if the key is not pressed at the same time. The sound of nitro consumption works the same way, so if you see the graphical effect but don't hear the nitro sound, you stopped pressing the nitro key too early (but note there is a 0,1s minimum delay at the end if you go over the min time).

The optimal play is to press the key exactly as long as the min time. This is obviously impossible, but if you manage to do it +-0,1s (the exact time is 0,53s) you should go faster than before.

My WRs were done before the discovery of this bug. As on a 2 minutes IL-race, this can mean 5 seconds more with nitro active, and so one or two seconds may be won with this.