I am curing a 25lbs ham and will cook it a day in advance to eat the next day (that day will be hectic so I can't cook it that day). Should I pull the hot ham and cool it down and refrigerate it and reheat is 20 or so hours later or should I keep it warm at 140F for 24 hours?
It's really a matter of opinion, but I expect keeping food hot for 24 hours will not result in a nice texture, or a nice electricity bill.
You're going to either leave it uncovered – which will result in it drying out – or cover it – which will increase the temperature and continue the cooking process.
I have no experience cooking a quantity of meat that large, but I'd suggest cooking it fully and refrigerating it quickly afterwards. The next day, get the oven up to high temperature (like 230 C / 450 F), put the meat in*, and then turn off the oven. You will hopefully get enough heat to warm the whole thing over a couple of hours and crisp up the exterior again, without overcooking it.
*Obvious warning: if you're using a glass dish, don't put it directly from the refrigerator into a 230C oven