i asked benzo users, they said they never know when they blacked out. one said you can never calculate the timing when i will black out. so i wouldn't suggest this to anyone. it is just complicated to make SN method more peaceful.
Depends how much you take. More likely to black out from Xanax then your are Diazepam. My suggestion would be to do a trial run first, take a Benzo and see how you react.
Not a good idea to take a load of Benzos before SN, just enough to make you feel more relaxed/calm but without blacking out.
I can take 1mg of Xanax for example and won't black out at all, just feel calm/relaxed. Whereas if I take 2mg then I'm likely to black out.
Diazepam I don't black out at all, even when taking quite a high dosage. Diazepam usually kicks in after around 15,/20 minutes.
Think it's a case of experimenting a few times first to understand your tolerance.