How does one know when Pretreated/Pressurized Wood is ready for staining/painting? I want to treat my backyard steps and fence and need to know when it is safe to do so.

Pressure treated is one correct term and I have not heard Pretreated used to describe wood. With PT we usually wait until the wood is at least 6 months weathered. You can also test by splashing water on the wood. If the water beads and falls off you can't paint yet, it needs to be able to soak in.