I made these, stuck them in the oven at 200 degrees, and forgot about them! They were perfectly hardened like, 6 hours later! I don't think you can overcook them at that temperature.
LOL I did exactly the same thing..6 hrs to the tee..I left the house at about 2.5 hrs and accidently forgot about them. I practically ran in the door freaking out thinking that they were going to be burnt and ruined. But, no, they were perfect!