Cumberland to Pittsburgh in one day

I floated this out there on Facebook and seemingly opened up a proverbial can of worms, but does anyone have any experience/advice for trying the entire GAP in one day. I may attempt it in summer 2019 if I can get the fitness. I'd be okay with delaying it a year if need be. The mid life crisis will still be there.
Thank you for any and all advice! Kevin

Kevin--I have the experience, and my advice would be... DO IT. I have done it in both directions, as well as part of a nonstop venture from Pittsburgh to DC. Was 55 years old at the time.
Please everyone, let's not debate the merits of "why would you do that...You'll miss all the scenery". I agree - - you will miss a lot of sights. But that is not the question that was asked.
It is very doable if you're in decent shape. You need not carry a lot of supplies. With proper planning, there are plenty of places to stop along the way to refuel, etc. I carried only a hydration backpack and two waterbottles. Food was stored in the backpack.
I rode it on a hard tail with a smoother tire, because... That's what I have. Your speed will probably only be about 2 mph slower than it would be on the road with the same bike.
If I had to choose the direction... I'd go from Cumberland to Pittsburgh. Yes the 24ish miles to begin the ride will be 20-30% slower than the rest of the ride. But, it's out of the way in the beginning. I found the 60+ mile grind coming the other way from Connellsville to the Eastern continental divide to be a grind.
If you choose to do this mid summer, you should be able to finish before dark. But if you find the need to be riding at night, a small headlamp like ultra runners use is adequate. I added a small handheld flashlight when I went from Pittsburgh to DC thru the night.
If you have any specific questions... Please ask and I'll try to respond.
More advice... Go back another time and explore the things you've missed. There is a lot to see.

I know a couple that did Pgh to DC on a tandem in 24 hours. Or that was their goal at least. I think they were late by a few minutes. They had support, meeting up with their sag crew at designated spots.

Just the GAP alone is a very doable goal for most able bodied people. That is, if it is preceded by months of high mileage training. But if you're asking the question, it probably means you aren't ready... yet. You may even already have the endurance but what about neck or back issues? Saddle sores, nerve numbness in the hands, etc?

But yeah totally doable! Build up to some high mileage days and you'll know if it's for you. I could probably swing it but have neck issues that make it not worth the aggravation. I can have just as much fun putting in 60 miles at slightly too fast a pace while fully loaded. That's how i'm handling my midlife crisis.

One day to ride the GAP is a reasonable challenge. I would suggest Pittsburgh to Cumberland the last 23 miles is a easy down hill.
Ride on!