I'm confused, is it 50 pounds live weight or dressed? Live weight to me is before slaughter, it sounds like you are really talking about a dressed weight.
My experiences are all on larger pigs, between 150 and 240 using a "tank" roaster so, I don't know how much help I can be. The big one was roughly 26 hours. It had been raised by a dairy farmer and they brought back the out dated milk and fed it to the pigs, this one got the chocolate milk for its last two weeks, I was skeptical about it but, the first bite made me a believer! It was a grand wedding feast that my friends still talk about (25 years later)
The small one seemed like maybe twelve or so. It's been a long time, my memory may be sketchy.
These were not butterflied, the big one was stuffed with a bread sauerkraut mixture a long time family friend brought over the day before and helped get it stuffed, sewn and in the roaster, then it was all just waiting.
I guess that's not much help, sorry.