Join Date: Nov 2018
Location: Magnificently mountainous McBride in the Robson Valley
Stacked and stickered, under cover and not cooked in a shed, you can expect fresh wood to dry down to the Equilibrium Moisture Content of 12-14% at about 1" per year. So, drying from both sides, a 2" slab ought to be about as air-dried as it will get in 12+ months.
What do you want to make?
Burls have tangled grain. They are a nightmare for hand carving, maybe better for power carving.
I carved a western red cedar 2" burl slab some years ago. I have not gone out of my way to find another one.