The rule of thumb for air drying is 1” per year in log form. As stated before, it will probably rot by the time it is dry.
Most people turn them as soon as they can. Typically you leave the “rough turning” about 10% thickness, for example, a ten inch diameter bowl would be left about 1” thick. After the rough turning you again coat the end grain with anchorseal and set it back to dry. When the rough out dries (4 months – 1 year) you would finish turning it.
Turning green wood is much easier than after it dries. Some people even turn to completion using the green wood and allow it to warp.
The wood will “keep” in log form but not for an indefinite period. After a while it may start to get punky/spongy. I have kept some woods like pecan for a year before rough turning it and there were no problems.
It depends on your storage, the type of wood, and the time of year it was cut.
Bradford pear is very soft when green and tends to go punky on me sooner. I try to rough turn it within three or four months. For the maple you should be good for about six months or more. Note: once you have it roughed and dry to finish turn, then there is no time limit, if it is several years it is no problem.
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