K.I.
I work in a bakery and you can absolutely make them the day before and put them in the fridge but I suggest the freezer even, it will ensure your frosting stays on the cupcake as you placed it (no dripping or sliding off) and cupcakes only take an hour, 2 hours tops to defrost....so you can make them the day/night before then take them out of the freezer the morning of, when you wake up and they will be perfect!
~This is what our decorator does when she has orders that need to be picked up on her day off. Just FYI, you can buy a container with a lid if you need to from your local grocery store bakery for like $2, people do it all the time at our store...not everyone has a container to fit 20+ cupcakes with a seal-able lid, just go in and tell them how many cupcakes you will need it to fit :)