This thread has answers to basic questions:
Sodium Nitrite (SN) Method Introduction This document is a compilation of different sn information, members inputs, important posts related to sn, recorded suicide cases related to sn, different research on sn and so on. This document also give a full understanding of SN, what it is, how it...
sanctioned-suicide.net
This thread has information about SN stability:
I'd like to preface this to hopefully help people not make rash decisions due to the fear that their suicide method will go "bad" and they feel forced to take it before they truly want to. Freedom of choice means everything. There is a lot of misconception on here about how long both of these...
sanctioned-suicide.net
But to answer your question, it's a good idea to prepare at least 3 hours of solitude for yourself.
Of course, death will most likely come sooner, but it's good to have a margin of error.
Losing consciousness usually lasts up to 20 minutes.