It will take 30 minutes at 180 to 200 degrees F. minimum. You will need additives. The best potting soils have very little actual soil in the mixture. You'll need vermiculite, do not use peat, decomposed organic matter, mycorrhizae fungus, bacteria added to your soil (soil should not exceed 25% of the total volume), do not use sand. After mixing everything except the fungus and bacteria to add later... THEN bake it for half an hour. I should be nice to tell you that the smell is worse than burning BEANS. And lingers. You will find that commercial potting soil is better and easier and less expensive. Why do you not want commercial potting soil? I am very particular and very distrustful of commercial anything. This is one of the few things that can't be cheapened and ruined or made to be a detriment. We always learn mostly by mistakes anyway. Just write down what you are doing, how much of any additive, what the soil was comprised of (gotta have a soil test well would be beneficial), what the pH was, what water you are using, fertilizer regimen, what kind of mulch and how decomposed it was, the kind of pot, no rocks or gravel beneath the soil, what species plants you plan to use in that pot, how much light is available and does this fit with the plant's needs, with pH in particular. Raise the bottom of the pot off any surface to enhance drainage. If I thought I could make better soil for less or even equal, I would. But I KNOW this stuff and I would never plant pots without commercial potting soil...unless apocalypse happens. I HAVE tried making my own soil, never again. Too lazy, doesn't save money and the stupid commercial stuff works GREAT. Need a big oven or you'll only be able to do a gallon at a time. Industrial ovens, flash heat, bacterial killing lighting, air pumps to pull the air out and pumps to replace the air.