As others have posted, the status is usually valid for the remaining months for the year you were comped and another full year after that. Others have advised that the best time for requesting SPG Plat status match is March 1st of any given year as you will get comped for two full years.

For me, I was going to re-qualify anyway for the year 2009 from my stays in 2008 so the timing didn't matter much except that I want to start my immediate SPG hotel stays with Plat status.