When you get to port on embarkation day, you will be assigned a dining rotation. There are 3 different dinner rotations, and each one has you dining twice at the first restaurant.
For example: the rotation we had on our 4 night was APLA, so we ate at Animator's Palate, then Parrot Cay, then Lumiere's, then Animator's again.
So it just depends. You'll just have to be a little flexible with how you pack. Or, if you really want to get dressed up at Lumiere's, you can plan to definitely dress up once, and then if you happen to get the LAPL rotation, then you can just go casual for the second Lumiere's visit. (or Palo's is also a great idea for the secon night!

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HTH
-Christal