As I think back, I washed my aluminum upper with brake parts cleaner, pre-warmed it, and sprayed a very light coat. When it dried, like a half hour, I sprayed another final cover coat and placed it in the oven at 150F. I let it cool to the touch with the oven door open and was done.
I've only airbrushed DuraCoat or Cerakote since then, so don't know if it's changed any in 24 years.