We did not go with our original date for our wedding, we had it one day earlier. We did this because we had specific locations we wanted for 3 parts of our events, and we had to be flexible in order to get all of them on the same date. The WP and Living Seas we had no trouble with but the UK Terrace (at that time you got the whole thing!) was booked on Saturday, 12/7 (1996), so we got married on 12/6. If we had been more flexible about Illuminations (other locations were available - we wanted UK) we would not have had an issue booking for our initial date. We knew about this at our sales meeting, which was 12/15/95, and left having said we want to go on 12/6. At 8 months out we got our contract and confirmation that our locations were all booked.
As for the time - this may have changed - but they used to do weddings (at the WP) on the even hours (2, 4, 6 etc). This was done to allow rehersals on the odd hours, and allow floral time to prepare for each event. Again, this is a long time ago and may have changed, but the time may not be available. Maybe a more recent bride can help? Funny, we actually picked an earlier time than our original idea - we thought 6, Lynn recommended 4 because we wanted dinner, dancing and then Illuminations. If we had started at 6, and Illuminations was at 9 that would not have been enough time. This also led to a very special part of our event, when Illuminations got postphoned until 10:30 that night, we were given special seats for the Candlelight Processional as part of our wedding event as they were concerned about the gap between the time reserved for the DJ (we had him from 5-8, assuming we would then go to the UK to have dessert by 8:30). Barbara Eden was the hostess and we got a special introduction and wishes from her, and then the rest of the crowd. A goosebumps moment that only FTW could deliver!