60 psi is what I use.
Length depends on the product, but go over just to be safe.
Heat is a factor and on hot summer days your resin will set faster (also less open/prep time)
The pressure compresses the air bubbles to microscopic size. Once the resin hardens those bubbles are permanently small and not visible. That is how you get clear resin. Sometimes big bubbles get trapped and not compress enough so you will end up with "redesigns" especially if you are doing hybrid blanks or if your blanks are not bone dry.
A vacuum chamber removes the air bubbles all together, so you don't risk having some in your cast, but the process is much longer.
