If someone else wants what you want, 11/12/17 is when the day and options are no longer available. Here's the explanation of the lottery from my PassPorter:
If more than one couple wants the same date, time, and venue for their ceremony or reception, a lottery is held at the 12-month mark. Usually only the Wedding Pavilion is in enough demand to require a lottery, although other locations may inspire one on popular dates. Requesting a Friday or a Saturday will also increase the likelihood that you’ll end up in a lottery.
Initially, the lottery is based on ceremony time. Although there may be only two couples who want the same time slot at one venue, every couple holding a wedding there that day must be entered into the lottery because the couples who lose that coveted time slot will need to be scheduled at their second- or third-choice times. Even if a couple gets their first-choice ceremony site, there may then be competition for their reception venue, meaning the times could shift again depending on which is more important to them—the ceremony time or the reception venue. If you will be entered into a lottery, you’ll need to consider your priorities. It’s a good idea to give your Wedding Consultant a few alternative combinations of date, time, and venue.
The lottery is held 12 months, to the day, before the event date or on the first business day following the date if it falls on a weekend. Your Wedding Consultant will notify you of the outcome on the following business day. After the 12-month mark, no lottery is required. If the site you want is not being used by another group, Disney’s Fairy Tale Weddings will request it from the central scheduling office and receive confirmation within 48 hours.