I would wait about a month before leaving them alone together. Thats just how I do it usually, especially with my foster dogs because you never know how a dog will react if they've never been exposed to cats. Even if they're fine at first, things can change when people aren't around. I don't know if Wylie is used to cats or not though?

Anyway, I'd wait about a month then just start leaving them for short periods until you feel comfortable to leave them together alone longer.