Can anyone give me suggestions on how to get a pair of mickey mouse ears to stand up using fondant that I did not dry days before? I thought about putting cardboard in between the fondant. 

knead in a lot of cornstarch

I have actually done this myself, just completely forgot to make the ears in advance.  I used cardboard and completely covered it in fondant. 

How big do you need them and when do they have to be ready?

 Normally I would use gum paste and put it in the oven with just the pilot light on. It dries overnight.

 Just put a thin layer of black gum paste over a small upside down bowl (2x) and one layer over a bigger upside down bowl, all covered in cling film. Release the next day once dried, glue together with edible glue - done.

 If you use fondant mixed with cmc or gum tex it will take a bit longer...

Thanks 

I have used gumpaste with extra gumpaste powder and cornstarch kneaded in.  Dries almost faster than you can work it.

Lots of tylose will work, I can get bows done just hours before needed that way. If you don't have any I think cardboard would be your best option :)