4lbs of nitrous in one night isnt anything to go home about.
I was putting 30lbs of nitrous through my car every other weekend. I have thrown 10 bottles through it in less then 8 months. Guess what? Im not redline tuned.
and BTW, doing dyno pulls on a nitrous car WITHOUT pulling out the plugs and checking them, is bad. A GOOD tuner, will do a pull, then pull plugs and get a ACCURATE reading. With nitrous cars, you cant just go by a dyno wideband reading. It might be fine at first, but its not nearly as accurate as reading actual plugs. My tuner pulled plugs and the thing runs like a rapped ape on the bottle.
you can tell the timing by the heat strap on the plugs and the heat range on the porcelain.