We are on the TA Celebration cruise in November. We had a similar problem with booking the steakhouse. The times started at midnight and proceeded in 30-min increments which of course we knew to be wrong. I called this to John Heald's attention through his FB page and he forwarded to IT which fixed it in a couple of days. We were then able to correctly book our time.
This might be what's happening here as well — just an IT glitch. When I look at our sailing, the times for Teppanyaki dinner are only 5:30pm, 7:15pm, and 9:00pm. You might try booking just those times (as the previous poster also reflected) if you can. And, then see if it will let you check-out. Perhaps someone can report this to IT as well for them to investigate and get fixed.
Have a grand trip!