Wear shoes and pants when doing this and work over a table. Heating metal always has risk of danger. Ie: dropping hot metal in your pelvic area doesn't sound nice. Follow manufacturers directions
Now do as the manufacture says. It usually says bake at 350 degrees for 20 minutes. That's the norm. Smaller ones may need lower temps longer. .
After baking let them cool then paint your eyes on with vinyl paints for a no chip finish.