I bake my kids projects on 110 C for 30 minutes.
I had also expressed an interest in using some of their stuff to experiment with a metal wireframe with them and, while I haven't gotten around to it myself, my 10 year old jumped on the idea and I had to make some for him. Not the most detailed mini was produced, but it did seem to work. Maybe experiment a bit before doing this with somethign you spend ages on.
I had pinned the wireframe on a block of wood and it all seemed to work in the oven.
Be advised: the fimo will not be hardened when it comes out of the oven. It hardens during the cooling proces.
Edit: yeah, I didn't read the question correctly.....