I dried the wood slowly in a cool, dry room before cutting the coasters. Drying in a room that has limited moisture and heat allows the wood to dry slowly and helps to prevent cracking. It took many months as I put them in the basement in the fall and pulled them out the following year.  I tested to see if the wood was dry but cutting an end section. Even with this process, a few cracked. I discarded those as I had plenty more to work with. I can't give an exact number of months to dry the wood for because it could take you more or less time depending on how wet the wood is, how fresh it is, and the area that you dry it in. The best method is to dry it until it is dry when you cut into it. Test and if it needs more time, then leave it for longer.