I did the same thing for a couple of years. 10.5 miles each way, often taking Friday off, a longer ride on Saturday or Sunday and resting the other day - either nothing or short easy rides.

I got to where I played it by feel. If my legs were still dead on Monday or especially Tuesday then I'd take Thursday off as well and the next week I'd be fine. That gradually shifted over to five days commuting and sometimes taking Friday off.

I think it's OK to ride as much as you want, but you can vary the intensity. And use common sense to avoid real injury.