Sliders can be made a few hours earlier, covered, and refrigerated until an hour before baking and serving them. Take them out of the fridge and allow them to come to room temperature before baking, or add a few minutes to the baking time to warm them through. Additionally, you can make the sauce and meatballs ahead of time or even the day before. Pack in an airtight container and store in the refrigerator until ready to bake or assemble.