How you plan to finish or reheat determines the cook plan on Thursday. If you have all options available and no time constraints on Saturday you can shorten your cook by 30-45 min on Thursday. Do not sauce the ribs. Pull them early, rest on a rack on a sheetpan on the counter for 15 min or so, uncovered, then put the pan in the fridge to cool completely; wrap the rib slabs individually in plastic, tightly, when cool. To finish on Saturday: For an oven finish, preheat the oven to 300 (no higher), unwrap the robs and place on a rack on a sheetpan. Place in the oven and reduce the oven temp to 275. Cook till done. Or, get your WSM going using your method of choice and finish the ribs in the cooker; keep the temps in the mid-upper 200s.
Note: In either case you will have to monitor the meat and cook till done. Cook time could be the same, less, or more than whatever time you shorted the first cook. Do not do the finish cook by time--test the meat for doneness.
If time or finish options are less available on Saturday then cook till just done on Thursday; rest an cool and wrap as above. Reheat in a 300 oven on the same rack/pan arrangement but with the ribs tented with foil; heat till just heated through. Or, in a pinch, nuke.
