As late as possible. During our last day at MK in November, the parks were a level 8. Rapunzel had waits of almost two hours all day and Cinderella had waits of 90 minutes. At 1:30am, we walked straight into both back to back. Within 20 minutes, we had met all 4 Princesses
Generally, it has been Rapunzel and Snow White on one side, with Cinderella and Aurora on the other side. Once during our trip in November it was Cinderella and Jasmine one evening.