A few nitrous questions

I'm seriously considering putting a 125HP shot of NOS (Holley) into my stock engined 5.0, but I have a couple of questions first.

1) Can I hide a 10 lb. bottle under the spare tire cover? Hiding everything else is easy, and I really want a sleeper.

2) How long does a full 10 lb. bottle last with 125HP jetting? I.E. how many seconds with the foot to the floor? Nitrous is definitely not cheap (just under $7 / lb. here), and I don't want to be filling it every weekend at $70.

From what I've heard, a stock 5.0 will keep together with a 125HP shot as long as it's running 92+ octane, and maximum timing is 5 degrees. Are those figures right? Last, about how much time would I shave in the 1/4? Thanks.