I just learned bout this today. some friends of mine swear by Ralph.... but here's what they told me to do.
once you have applied the crackle layer, you let it go for maybe an hour or til its dry??/
Is what I remember... But then the real thing they made a point of was to load up your brush with the paint tht goes overthe crackle, and use quite a big brush, because you never want to go over it more than just that first time with the cover paint. You apparently have just a very small window to apply it, before it starts to distureb the layer underneath.