How fast mescaline works depends a lot on what you've eaten, how much and how long ago when you take it.
LSD always takes around one hour for me to work, it might be 55 minutes or 65 sometimes, but it's never much sooner or later. The same is true for MDMA, wich alway takes about 35 minutes for me. It may sometimes be 32 or 38 minutes but it is never outside of that timescope.
Mescaline is strange enough totally different from that.
I gues that if it could be smoked or snorted, wich i never tried,it would work always immediately.
I have no idea what causes it but it must have something to do with how it enters the bloodstream. Maybe it can´t be absorbed through the bloodvessels in the stomach so it has to go through the bowls. It would enter the bowls sooner when the stomach is empty.