Since you're not actually correcting the paint in this case, then you'd only do it once the wax has gone and taken the filler with it (in this case, the Black Hole). Once every three months would be about right, but you might need to do it monthly on a car kept outside and used daily or six months when it's a weekend toy that barely moves and is kept indoors.
If you wash properly (i.e. NOT using the AG shampoo, as that strips all the protection) then you really don't need to do it that often, it's just how you feel about how the paint is looking.