I let mine set for a year. They make good cover for rabbits, etc. And if you are trying to get a wildlife exemption, they count as habitat.
I always plow around them so that there is barren ground around the pile. The stumps will take 24 hours to burn, some big ones 48.
All the other limbs will be gone in an hour. Do it early morning
when no wind and if possible when a light mist or rain. That's just to be on the safe side. If you have several, don't burn them
all at the same time. That's just me again being overly safe. I'll light one, let it burn for a couple of hours before I start another one.
Just don't lite it and head home as I have seen some "city ranchers," do.
Photo below was about one minute into the burn. They go up fast and hot.