This can be done the night before, or at time of serving. (sprint2thetable.com)
I'll do it on a day when the exact time of serving doesn't matter in case I need to play with the time. (trissalicious.com)
I took a few suggestions from others, namely I added some feta at time of serving and since I made the salad in advance I also held off on adding the fresh tomato until ready to eat. (epicurious.com)