I disagree with the other answers. Your pressure treated can be painted just after it has dried out a little with a porch and floor latex paint with NO PRIMER. Reasoning behind this is two fold.
1 if you prime it with an oil based primer you have effectively sealed in all of the chemicals in the lumber and there is no place for them to go so they peel and blister the primer and force it up causing a nice customer complaint. Latex paint breathes and allows moisture to pass thru the paint film while protecting the substrate. If you wait a year your wood will be cracked,split, and bone dry and you will need an oil based primer to seal it up but the damage has already been done.