Do I need to adjust the time in the oven if I am using three pieces of meat, two of them are at 2LB the other is 1LB. So it's still five overall.

I made it in my slow cooker using two boneless short ribs because I wanted a meal for one with a lunch size leftover amount. It still took 7 hours on low in my slow cooker. I would plan on the amount of time it calls for in the recipe, but be ready to take it out early if the meat is tender especially the one pound piece. It reheats beautifully, so no worries if it's ready before dinnertime.