I did mine this way:
Instructions are not mine, but from a guy from the Philips Lighting Forum.
Turn oven to 400
Now, count 10 minutes if you have a junky oven, and maybe 6-7 minutes if you have a newer, state-of-the-art oven.
After counting ten minutes(or 6-7 minutes) from the time you turned that dial to 400, turn off the oven right away
DO NOT FORGET TO TURN OFF THE OVEN
ONE MORE REMINDER TO TURN OFF THE OVEN – you will not like a melted headlight
After turning it off, place the headlight in for another 10 minutes. The oven should be cooling down during this ten minutes. You can check after five minutes and make sure everything is all right. But when it gets hot enough, you can use an oven mitt and take out the headlight, and you use a screwdriver and the headlight will pry apart with ease. Make sure to release the tabs.
Do not place the headlight close to the bottom oven coils, place it away from the coils but don’t let it scrape the top coil.