Can't help ya with setting up a schedule for shooting, LOL... that's gonna have to be up to you
Once a week should be fine, as long as you closely monitor the plugs and the tune... your best off to play with it at the local dragstrip. That way your results are accurately measured... and you can kill the motor after you cross the 1/4 or 1/8 to get a good reading on the plug, and make tuning adjustments accordingly.
Keep a close watch on your bottle pressure, maintaining a minimum of 900 psi is critical in achieving the proper nitrous fuel mixture, as well as your fuel pressure... get a gauge setup where you can see it while your spraying (pillar or cowl, typically). I like to have the nitrous press. gauge and fuel press. gauge right next to each other.
A fuel pressure safety switch (aka hobbs switch) and MSD window switch (critical on a stick car) will also add to the life of your motor while using nitrous oxide.