If you register and make three stays before Jan 31, 03 you will be silver for 03.
You might want to make some of the stays in January 03 if you think you may end up short of 15 nights in 03.
IMHO, the only real benefit of silver is the extar few % bonus on "real" Marriott stays. Only since I made gold have I gotten any upgrades and concierge floor access.