I am 15 minutes from the Montour trail. I am also close to the Pittsburgh airport. You could drop your bike at the airport and take the bike trail to the Montour or I could just pick you up. I would think the Pittsburgh airport office would be open. If you wanted to make some miles then there is another campsite near Harmerville just outside of Library. That one is very easy to pass up!

Your next stop would be Dravo or stay at the Yough Shore Inn.
You will be riding through Glassport and Mckeesport the last half of your trip. I would highly recommend you do so before night fall. It is OK during the day and I would ride it at night only if there was no other option.
The bottom half of the Montour is full of detours but it is not too bad. It gets better all of the time. The very last part of the trail is road. It is mostly back road. Not much traffic at all. Crossing 51 can be pretty bad. But with no tour guide, I am not sure if I would recommend if you are pressed for time. When I made my tour of the GAP down the Montour, I made a bunch of scouting trips and it took me a little while to figure it out.
Too bad you can't come on Saturday. I am just getting off a two week vacation (tour around Lake Ontario) and might not be able extend it to Monday. I would have been able to act as your tour guide.
Another option would be to take the Montour from the airport to Library, PA then take the light rail (we call it the T) into Pittsburgh. IMHO the prettiest part of the Montour anyway and rivals much of the GAP.
There is a campsite at Boggs. It is not far from the Pittsburgh airport. You could drop your car and take the bike trail to Boggs and camp overnight. There is no water at Boggs but I could probably drop off a gallon for you.
One option might be if you can even get here Saturday night. I could pick you up at the airport, you crash here and Sunday morning you would have the above two options or go through the city.
If you have not been here it is well worth seeing. We have the inclines, the bridges, 3 rivers, lots of great architecture and the bicycle museum. If you left Sunday morning from here you would have time to see most of it if you stayed at Dravo campsite or stayed at the Yough Shore Inn. I highly recommend staying there. It is best I can describe as whimsical and Lynn's personality is all over it. She is a hoot.
Let me know what you decide. I might be able to make some changes. I will be back from Lake Ontario that Wednesday.
PM me for phone numbers.