I believe that you will want to change after dinner. This time of the year the humidity starts getting up there and for me wearing slacks in that kind of weather just isn't going to happen (except for the WD Theater shows and dinner).
We had late seating an here is what the guys did. We wore polo shirts and slacks to the non formal non tropical/mexicalli..... dinners. After dinner these evenings we just changed into shorts and were ready to go. Since we wore our shirts for a short period of time that evening, they were still pretty "fresh" (didn't go into areas where it was smokey and it was not to humid outside). This was the shirt we started the day out in the next morning. It cut down on the amount of clothes that were needed (only 1 1/2 to 2 outfits per day instead of 3 -- daytime, dinner/evening, late night).
I would not do this during the heat and humidity of the summer / early fall!!