Apparently it takes longer for bud to yellow than tobacco. After 2 days there were only a few yellowing areas but after 3 it's getting substantial. I'd say 4 or 5 days total should do it. Small fluff buds yellow first but the big ones soon follow. And surprisingly no mold at all so far. I do have to open the container and rearrange things though, to let any condensation dry off some and to have them all get in the middle of the pile sometimes. It does seem to increase potency too, judging from a few tests as it progressed. After about the first 36 hours I could notice increased potency.
What I used for this was a long container big enough to lay out the heating pad in. It's not a very high container, made to go under a bed. Anyway I put the pad in there first then a layer of folded blanket then a later of some poly mesh material which I just put in to allow more air under the material since I happened to have it. Then I put a layer of parchment, regular paper kind not silicone. I want moisture to be able to pass through it. Then I lay out the crudely trimmed buds, good ones on one side and fluffy lower ones on the other. That made a pile about 4" thick. I put another layer of parchment over the pile and put the lid on. I also put the probe of a meat thermometer under the middle of the pile, the kind that has a wire going from the probe to the unit with the readings on it a few feet away. That way I can monitor the temperature from outside the closed container.
I found that setting 1 on the heating pad was all I needed to get the bottom of the pile to 104 F. Every few hours I would open it up to rearrange and also wipe off condensation from the inside of the lid and the sides of the container, like about every 6 hours in the daytime. I also put a couple folded blankets over the top of the container, so it draped over the sides and ends to help retain heat.
It's a simple waiting game, doing the rearranging/wiping as required. Very pleased with how well this simple method is working. I guess it must be the heat that prevents mold growth. Haven't seen one speck after 3 days. The material is gradually getting more compact as it loses water but is still plenty moist, as it has to be to get yellow. Here's a pic of a couple bottom buds that yellowed up so far. As you can see, they look practically fresh, just lighter in color. The green is gradually being replaced by gold and there's zero mold. The smell isn't much different at this point though. May take a lengthier aging/fermenting period for the aroma to change noticeably. No ammonia smell at all yet either btw. Really the only differences so far are lighter color and increased potency, at least it feels like it to me. Didn't seem that potent when I microwave dried some fresh material. Maybe I can actually dry it in the container after the yellowing, by raising the heat setting and wiping the condensation at more frequent intervals. I like the fact that the container keeps the smell in and mold spores out. I may be able to completely dry it in there.