I hope you are well qualified in herding cats; you will need the experience.
Seriously, for a group that large you should tend to break up into smaller groups and only have two or three meals together during the trip.
Normally for a group that size to eat together you need to have your reservation either within 20 minutes of the restaurant opening for the meal, or within 20 minutes of the last seating for the meal. Otherwise you will not be seated together, or even at adjoining tables.
Based on the number of people served, a restaurant will not keep tables unoccupied to put together a group. Let's say there are three tables in a row, which together can accommodate your group. Table A opens up, and it looks as if it will be 20-30 minutes before Tables B and C are done. They will not hold Table A. But let's say they hold Table A. 20 minutes later Table C opens up. OK, they are now holding tables A and C open while waiting for Table B to open, but these people are taking their sweet time and planning what they are going to do the next few days. By the time all three tables are ready for your group, they actually could have seated a party at Table A who might be close to finishing their meal. In other words, they would rather fill the tables and serve meals and people get out than have tables sitting open waiting for a large group.