Where are you staying? If offsite, I would say Tues or Wed. If you want to see Spectro or FITS, see the park hours at the official site. Get there ONE HOUR before opening. I would make a lunch PS to get out of the heat for a while. Cinderella's Royal Table is very relaxing. You won't see it all and I wouldn't advise trying. You will miss soooo much and not have fun if you are on a "mission". Enjoy what you can. Depending on the ages of your party, you will want to do Fantasyland first (Dumbo FIRST)- for young kids-straight through the castle, Frontierland first (left) for Splash and Thunder Mountain, or Tomorrowland first (right) for Space Mountain and Buzz Lightyear. If you aren't staying far, you may want to take a swim/rest break after lunch and return to the park around 4( if they are open until 9).
Wear comfortable shoes,a hat and sungleasses, sunscreen, bring a squeeze breeze, and water.