Hi, Kevin!
Disney Cruise Line does have two different Main
Dining Room seating times. The first thing I'm going to recommend is that you
log into your reservation, and see if you can modify the dining time on your own.
Once logged into your reservation, scroll down to the Cruise Details tab, and the second one over should be Dining. There's a link at the bottom that says "Change Seating" that you should be able to click. It's going to show you the two dining times onboard the ship - Main Seating, which is usually around 5:45, and Second Seating, which is the one you are in. If you can change it, you'll be able to just click the bubble right in front of the Main Seating tab. It may say that the seating is at capacity, in which case, you won't be able to change it on your own. I encourage you to check back periodically because that could change.
If you get all the way to your sail date without being able to change your dining time, the first thing you want to do when you board the ship is to head to guest services. They'll be able to talk to you about your dining options, including switching your seating time if that's possible. They will do all they can to accommodate you.
Kevin, you can also either call or email Disney Cruise Line and let them know you have this dining time preference. It will be noted on your reservation, and if they can make the change before you board, you'll see it reflected on your reservation.
Fingers crossed!
Anna