Wouldn't take long. Building for Mac (or for that matter Linux) really is as simple as flipping a switch in Unity. The problem comes when all three builds are out and i have to keep all three up-to-date; that's why I'm keeping to Windows while updates are frequent. Once I'm out of early access, I'll be rolling out on all three platforms plus Android. (Fun fact: I've been setting up mobile stuff all throughout the updates you've been getting, just behind the scenes.)