Ash is a good insulator. I’ve had buckets that still had coals for several days.
I learned that the hard way. 2 day old ash in the metal bucket, and I spread it along the edge of the yard close to the woods. I never do that anymore. It was a breezy day and there were still hot coals in the ash, and it lit up the dry leaves. I barely caught it in time to get it stomped out before it got out of control.