Over the past 3 months I have cut down numerous red oak and white ash trees with the intentions of timberframing a house next July. My plans were to have the lumber milled during this month (October) and my timberframer was going to tool the joinery between the months of March and June. Does anyone have any experience with working with hardwoods which have dried over a 6 +/- month period?

Hopefully you've coated the ends of these logs with an end sealer. If not you should as soon as possible (if you need a website where you can get some let me know).
This end sealer will help to prevent the log ends from splitting as they dry.
Once the timbers are milled the end sealer will force the water in the timber to evaporate threw the faces of the timber not the ends. This will help to prevent end checking of the timbers.
Having your logs milled now for joinery six months from now will make them a little harder to work with. What does your timber framer say?
If you could you should try and mill the logs close to the time when they will have the joinery cut, thereby making them as fresh as possible. Fresh wet hardwood logs will be easier to cut the joinery in.
Good luck with your project. Jim