Well, I think their writing sessions would largely be dependent on when the individual member's side-projects/solo albums are done recording/mixing/mastering... AFAIK, JLB, JMX and JP are working on things right now, while MP is touring for the better part of the remaining months this year. They'll probably want to take a break in Nov/Dec/Jan before they do anything, so the earlier they'd start would probably be Jan/Feb 2011.
If the individual members wanted to tour for their respective projects, it'd give Mike some time to record with other performers (a new Neal Morse album perhaps?) and projects (SW and MA?), so then that'd take the rest of winter and all of spring, so then writing wouldn't begin until summer 2011. They'd probably write til August, then release in late 2011 around the holidays, then begin touring in Jan/Feb of 2012.
Worst case scenario, they begin writing in winter 2011, and release late spring 2012, and tour in the summer (European festivals, maybe Progressive Nation '12), then in the fall (NA tour leg most likely), break in winter, then continue touring through 2013.
-Marc.