I'm making a cake with relatively heavy and straight fondant accessories standing out of the top. I made them three days ago to let them harden appropriately but disaster has stricken so I had to re-make them and delivery is in two hours! is there any way to dry them? I've put them outside for about an hour (its dry and sunny-ish) but can I put in the oven or something to make them hard in time?
You need to use gumpaste to get anything to dry in 2 hours.
Try kneading in Tylos into your fondant. It will help dry it out.