If you want SN to take effect quickly, you must have your stomach as empty as possible, this does not mean that you go 24 hours without eating. 8 hours without eating and 2 without drinking is enough.
How long does xanax take? I didn't know. In the guides they recommend taking the benzos right after SN, but I don't have confidence and I will take them 20 minutes before, crushed (which will help their absorption) maybe with xanax it will work too, by crushing it and diluting it in water you will drink less, like I mean, the less things in the stomach the better.
Meto should not be avoided, precisely because it blocks dopamine that requires a prescription and is so good for preventing vomiting.
If what you want is to fall asleep early, according to several cases, in less than 20 minutes (following the instructions carefully) you will be unconscious due to NS. Also if you are not used to xanax it should not be necessary to take that much (unless you want to get KOed) I will use 3-4 mg of lorazepam, and I am used to it. Find a comparison table to calculate how much xanax those 4 mg of lorazepam are. I weigh 70 kg and I have a tolerance, but if I take 2 I usually feel quite relaxed, maybe you don't need as much xanax.