Depending on how much you want to push yourself you can do it in two days. Depending on where in Pittsburgh you are going. I traveled from McKeesport to 20 miles past Cumberland in two days without a lot of pushing. The surface should be fine even with the rain, I would be more worried about the cold. I was in Frostburg today and it was COLD imo. Cell phone coverage is spotty between the Eastern Divide and Conellsville, there is a cell booster at the Rockwoods visitors center.
I suggest make a plan on where you are going to stay each night and shoot for it. Also call ahead to where you are going to stay, a lot of places are shutting down for the season.