Nitrous delay

Purge kit is not the answer here. A delay of 2-3 seconds means you have a serious issue somewhere, and purge kit would just mask the problem, if it helped at all.
At 100hp jetting, you should be able to make your three runs with almost no noticeable delay or hesitation.
Go over your system again to make sure the switch is being properly activated at wide open throttle every time. If you really have to shove the pedal into the floor that last half inch, it’s probably not activating the switch on acceleration, so simple adjustments may fix it.
Also check your tune. Nine psi at the nitrous system fuel solenoid is probably too high at that low power level. If so, it’s too rich at first and bogging down, same as having air in the nitrous side line.