You should let the blank soak for at least twice the length of time you had them under vaccum. 2 hrs under vaccum, 4 hours soaking.
Double dying is where you have two different colors in the wood. There is different ways of doing it. You can soak the blank in one color for (??) Hours/minutes, cure it, then switch colors and do that color like you would on a normal blank. (Pull vaccum until bubbles are gone, soak it, cure it) Soaking it will get the color into softer parts of the wood, and the vaccum will get the other color into harder parts of the wood.