Some people find a lot of peace of mind buying the plan before the 6 month mark. I find this especially beneficial for people who tend to obsess - we go over everything far in advance of the sway and it just is a lot less tension filled than waiting till right before. We do have a renewal option where you can renew the coaching at a much lower price or it's worked well for people to get it all ironed out during the 6 month period and then just anything that comes up they can use the free forums or PM me after it expires.
I just think that trying to time a "perfect" 6 months to exactly coincide with when you want to TTC is a teeny bit Martha. :)