If these are bone in normal size shoulders you wouldn't be starting them Sunday morning anyways, they'd never be done in time. Plan on 1.5-2 hours per lb at 225 and definitely err on the side of caution in the case of a long stall.
Throw them on the smoker Saturday night giving yourself a 3 hour extra window and that way you can wrap them in towels and rest them in a cooler for whatever time is leftover before you need to pull the meat. You got this.
For smoking just about any large piece of meat, this is my go-to strategy for any occasion, even if it's a supper time engagement. With the chance a varying smoke times, I don't want to be apologizing to guests (or even just my own family) when the cook is taking longer and then I am thinking about rushing the meat to the finish. Which I have done.
Now I nearly always start the cook at about 9pm the night before and it's basically guaranteed to be done by the AM or noon at the latest. I can do the cooler trick or serve it for lunch. Sometimes if schedules do not line up I'll cook the meat a day or more ahead of time and reheat it later. I don't think most people can truly tell the difference if you follow the steps below.
Also since I have a large smoker I almost never smoke just one pork butt -- I'll do a second one and pull it with the first one and throw it into a big ziploc bag or two for future leftovers and freeze it. If you want you can even vacuum seal it if this is something you might store for awhile.
So for your reheating instructions, cook the meat when you smoke it in such a way that you can trap as many of the juice / fat rendering and save it. I do this anyway to keep grease out of my smoker. When you go to package up your meat for the freezer, pour that gold into the bag with it. Then when you reheat you'll have some trapped juicy goodness to make sure it's moist when you re-serve.
As for reheating, the best way is in a covered container of some kind in the oven or pellet grill at like 300-350F for 30min to an hour, just until it gets up to 145F or so to serve.