I don't see why they can't do what other slams do, start at 12 and schedule 3 matches, but say that the 3rd one won't start before 6pm or so. As they said last night during Djokovic v Hurkacz, it must be very frustrating for the players having no real idea when they will start, and then by the time they did start they are already thinking this match won't get finished tonight.
I watched that match and it was clear that Azarenka waved her racket, commentary team all spotted it too. I did see one tweet from someone who saw Azarenka wave, but didn't see Svitolina respond due to the umpire's chair being in the way. Obviously the whole crowd weren't unsighted like that though.