Tough question. We had CM booked for our first night when we went to WDW in December. We had gotten up at 5:30 AM, spent the afternoon in the parks, and had reservations around 8:00 PM. The problem with our reservation time was that it was super backed-up by the time we got there and had to wait until around 8:45. By the time we sat down, I was miserable and really just wanted to get back to our room and sleep, so I really didn't eat anything or participate all that much. I usually have a lot of fun at CM, but that time was not one that I really wanted to remember.
If you guys are doing a lot of running from one thing to the next all day, I would skip it, but would definitely not make a final decision until you get to WDW. You can always cancel if you get there and decide that you guys are too tired. However, I would recommend that you all should try to take a nap on the plane so you can experience it. The food is nothing to write home about, but the experience is definitely worth it!