IIRC there ain't no gasket. Silicone...aka "liquid gasket". Rarely leak, actually I can't recall the last oil pan leak I saw. Rear main seals? Different story. Done plenty-mostly on the early ZD326's. And yes the engine's got to come out to R&R the oil pan. That or start cutting on the frame for access...your choice. Easier to just pull the engine, IMO.
If someone can do it in an hour, I need a good tech.....but when I say "good", I mean if you can do this job in an hour and it be good QUALITY work (no loose bolts, low fluid levels, scratches, dents, dings, etc).
It's about 3 hours from the time the tools come out til the time they go back into the drawer. I think Kubota's flat rate is around 4 hr if I remember right, and they figure that on a machine that's squeaky clean (new) with zero hours runtime on it, they do it 3 times in succession and then average the times. My goodness after you do it the 2nd time you should be good at it. But if you do one every 5 years, not so much.