I found the Behr time recommendations interesting. I know that Acrylic paint dries then it hardens which takes quite a few days. Make sure your son is careful about painting art on it with cheap craft paint. They can break down with water over time whereas artists quality acrylic paint is just made with more quality and that needs a few days as well to become water proof.

If you get water on an acrylic painting that is dry like a few hours, it will make a water mark. Two days later you can run it under the faucet. And according to Behr, the hardening process probably goes on for quite some time. No doubt the formulations all vary but 30 days before scrubbing is very interesting.