I'm so far from goal I think I'm actually going backwards
so I can't speak from experience, but what I would do, personally, is once I got within 3-5 pounds of goal, reevaluate. Ask yourself things like, does this weight look good on me (ha! We all know any pounds lost look better than before, right?), have I been losing consistently or has the last few pounds been a REAL struggle, do I feel like I can maintain this weight? Then decide if you want to change your goal.
Although I'm sure they'll be glad to sell you additional weeks if you want to lower your goal, when you reach your initial goal you can always go into stabilization/maintenance for X months that you've paid for, then after you get your rebate (if you qualify) you can tackle that last X pounds.