You used to be able to make them as soon as you boarded for the entire cruise, not anymore. They can be made the day or or day before only. If you go to the reception area as soon as you board (within an hour or so) you won't have any trouble getting them. it is toward the end of the cruise when people want to try the specialty dining rooms or are getting tired of the main ones that it gets a little harder. I would recommend Le Bistro for sure, followed by Cagney's and Mama's kitchen. There is no charge for Mama's kitchen.
Nita