Klpca,
You've already received very good advice so I won't add to that. Rather, I would point out that just because there is this "supposed" deadline doesn't mean it is a never again, deal. I can think of many situations whereby Marriott MAY (not will) come up with some limited time offers to goose enrollment, or will allow for the purchase of "x" points the ability to enroll, etc. Fact is, a deadline gets people to act, then a limited time offer gets a few more off the fence, etc. These are all very common marketing tactics that get applied in different industries, over and over again.
Given your, korndoc's and many others current usage, single weeks status, etc. not enrolling isn't the end of the world. I enrolled and am very happy with the extra options as they fit our needs better at this time. I say, enjoy your week, and keep an eye out for other offers to enroll. Who knows at some point you might be in the market for an additional week and the option, if available, will be more appealing then.
I wish you many happy vacations !