I start with a preheated oven.... Usually around 400 degrees... Then I PC the part and toss it in the oven. Just about the time I finish mixing a rum and coke and light a smoke, I return to the garage and find the part just beginning to "flow out", That's when I hit my stop watch and grab a chair. My timing then works out to be about the time I finish my second smoke and almost polish off my rum and coke, the part is DONE.
Check the maker of the powder and see what they recommend. For mine, It's two smokes and a rum and coke!