Old Hotpint

Question

I have an Old Hotpoint, built-in, electric, self-cleaning oven that I had installed when I built my home in 1987. Still works GREAT. I am selling the house and would like to replace the metal racks...as well as the plastic button on the clock is snapped off (didn't know my own strength..ha..ha) Also..how long do they normally set the self-cleaning mode for?