Based on my very limited experience, this is my guess.
I’m a technically adept and mechanically inclined person, who is not prone to panic, but I have essentially zero flight experience. Anybody with any piloting experience might be a better choice than me, but if the rest of the plane is full of people returning from the “VCR still flashes 12:00, and its 2021” conference, then I’m probably the best bet to land your plane.
My flight experience consists of playing flight sims in the 80s, talking a lot with a friend as he earned his piloting license, and about 15 minutes at the controls of a glider. What that 15 minutes taught me is that even though I knew to “step on the ball” flying a real plane is extremely different than a PC based flight sim. Sure, the instruments are the same, but the planes response is very, very different. On the PC, the tiniest joystick movement did a lot. On the glider the center stick had to be really pushed around to get any response.
It also showed me that it is very difficult to do things like locate the airfield from the air and to get the plane to stop turning and pointed at what I want. I can imagine a glider is easy mode compared to a 747. (Even if the 747 has automation to maintain coordinated flight.)
So, based on that, I’m going to say that flying by hand is almost completely out.
However, I may be able to setup the plane’s autopilot to do things, and once lined up with the runway, to execute control inputs at the right time to do things. For example, when crossing 10,000 feet lower the landing gear, at 5,000 feet move flaps to position 4 (or whatever).
So, say I’m over the middle of an ocean, plenty of fuel, but no pilots. Perhaps I can be instructed on how to setup the autopilot to get me to an appropriate airport, and then be talked down. There is lots of time to do dry-runs. So, “find this control, later you will turn that knob to this position”, etc.
So yeah, if anything goes wrong, we’re all dead. But if all I need to do is get the glide slope setup, let the plane touch down, and then hit the brakes, there might be a slim chance.
I think the first obstacle will be convincing the people on the other end of the radio to give me a real destination, and not just ditch me in the ocean. (I think that was the plot point in a movie.)
So, how long to orient a motivated newb to the cockpit of a 747? How long to talk through the landing procedure in detail, with time for questions? How long to talk through several dry runs? I’m guessing at least 3-4 hours, but absolutely no guarantee of success. Maybe better to try and revive the pilots with some prescription drugs found in carry on bags, and some energy drinks from the galley.