Why season the timbers at all before cutting joinery?
Timber framing was created in relation to the use of hand tools and therefore freshly felled timber. Millions of Timber Frames from the 12th century on have been built utilising green wood and are still in use today.
I would assert that the selection of trees and proper sawing are much more valuable in reducing twist, and other defects than "curing."
If curing was to be used, it would be more appropriate to utilise before the timbers are sawn, since sawing them twice would take a huge investment in time and energy.
In my shop, I would begin cutting the frame directly after the sawing was finished. At the same time I would sticker them properly in all phases of the project, apply Anchor Seal to the end grain, and cover them with sheet metal or some other material that would not restrict air circulation. You could also just let them grey in the weather, preferably out of continuous direct sunlight.
On this subject; Jack Sobon's Built a Classic Timber Frame is an excellent resource.
-Collin