We often travel this time of year. I make "Have To" PSs, most notably the CP Dnr Pkg. We tend to eat our large full service meal for lunch and a lighter meal for Dinner. I call Dining prior to leaving the room that morning, once we decide which park we will visit that day, and have always been able to get a seating time within 30 minutes of my desired time, except once. I always have a "2nd choice" restaurant, just in case, but like I said I only used it once.
However, Le Cellier for Dinner does seem to book up in advance, so if that is one of your choices, you may want to call for that.