The usual NOS setup that ASR Engineering installs is a 20lbs. bottle.
Now how long a bottle lasts depends on how much you spray, how long and how often.
This is a short version to explain the setup.
Now the system runs on its own software flash created by ASR and installed by Active Autowerke. This is in addition to whatever ECU software upgrade you may already have. This manages the nitrous delivery. You can have the system off and you can have the system on but drive around normally and no nitrous delivery unless you go WOT.
The system is designed to spray when you go WOT and shut off the second you lift.
It is up to you and how often you go wide open and for how long you sustain WOT. Usually it is very short because there are no areas you can sustain such distance and speeds.
The 1/4 mile strip is about the only place to allow you such distance, time and velocity.
A rolling start from 60 mph and run to 180 is very short.
After the initial novelty wearing off (it is a blast) and you become judicious with the use, a bottle (20 lbs) can last about 5 to 7 days.
A bottle refill is $50. BTW the system has no leaks.
Regarding the E60 M5 accept no other NOS setup except one designed by ASR Engineering. If you have any more specific questions feel free to call Abid at (786) 258-0009. Abid will travel to you to do your install.
The system is totally automatic. Bottle opener and closer is automatic.
This was the M5 back in January. Abid and I are taking the car back this month and lets hope for better results.