I went ahead and emailed Marriot. They said I can start the challenge in late December to get my Dec 31st stay to countand still have status though Feb '15. With that I have 8 stays for trips I'm already taking to Europe and China. I'll take my gf to Portland or Vancouver for a weekend to get my other stay to qualify for Plat Challenge.
Currently at Marriott South Beach in Miami and enjoying it. Wish I had Plat status now though as the lounge view looks pretty nice.