My recamend:
1st pass run without the bottle, read plugs check everthing out, etc.
if everything is good run a pass on the lowest setting on the n20 kit (lets say 100 shot, no need to be a hero on the first run), take timing out, and only spray on the first 2 or 3 gears, get out of the gas and spray, kill igntion, coast off the track, pull a plug or 8 and check it.
if everything is good work your way up with spraying in higher gears and more spray, and when you end up at the setting of N2O your are going to stay at then start fine tuning the timing.
I highly recomed getting a nootbook to log everything (jets (carb and n20), air temp, timing, track conditons, etc) even a dig camera pics of plugs to cooralate to your setups.
if you have a probem with your setup it is much better to find it spraying a 50 shot in 1st gear than 200 shot in 4th gear. If you hear anything bad or does't feel right, get out of it, its not worth losing an engine over.