We don't need to do anything to Aquasol HVP and we do not add diazo. Since we use emulsion to blockout a post expo is necessary for that but the stencil itself doesn't seem to need it at all.
Hardener is more of a helper/security blanket on long, long runs and it takes a whopping 30s-1min to apply when you feel like you need or want it. I use it primarily on flatstock runs with the more aggressive WB inks and very thin stencils there.