As another quick FYI, if you buy EBCI and later on your flight time changes, make sure to contact Southwest Customer Service and ensure that your EBCI was properly transferred over too.
My family of four found this out the hard way when we took a trip in March of 2017 for which I purchased flights and EBCI on the first day of release (which was in August 2016). A couple of months after purchasing the tickets, I got an email that our return flight home had been pushed back an hour. I noted the change and didn't think anything of it. Fast forward to us checking in at MCO for our flight home. I hadn't checked in online prior to that because I had purchased EBCI on the first day the flights were released and would likely have a mid to high A-range position after being automatically checked in 36 hours prior to flight time. Or so I thought.
Colour me surprised when our tickets printed out with boarding position in the very high C range! When we asked the SW rep at the luggage check-in counter what had happened, she looked at our account and said that, yes, she could see that I had purchased EBCI but it had, unfortunately, not been applied properly to the new flight time and there was nothing they could do. Then, when we reached our gate, we spoke to the customer service rep there and she reiterated what the first rep told us - when the flight time changed, the EBCI didn't carry over (even though they could still see it in my account), so I would just have to accept the crappy boarding position and, if I wanted my EBCI money back I'd have to contact Southwest myself. They were unable to rectify this situation in any way at the airport, which seems ridiculous to me and, when I suggested that we would be happy to board the plane after family boarding in lieu of getting our correct EBCI boarding position, they would not even consider that. We ended up being dead last to board the plane, just behind another family of four who had also purchased EBCI before the flight time had been changed.
Luckily we were flying home mid-week and the plane wasn't full so we were still able to sit together (albeit in the very last two rows of the plane) and I did ultimately get my money back but it was certainly an unpleasant way to end a great Disney trip.
Moral of the story: If your fight time is changed, double check that the EBCI is showing up properly on the new time!