It depends on a number of factors, but I've heard of people who score tickets after showing up as late as 11am. Obviously, the sooner you show up to the line, the greater your chances. Also,since TotS will have only been in performances for 3 days upon your visit, you should be able to get tickets at that time. During previews is the easiest time to score tickets to Shakespeare in the Park before the press starts to publicize it.
"Mostly, I loved the size of these people's emotions. Nobody has emotions this size anymore. Outsized emotions. Operatic emotions. Kushemski and Vanda are like Tristan and Isolde, they're Paolo and Francesca. Nobody's in total thrall like this anymore. Nobody's overcome by passion like this, or goes through this kind of rage." Thomas, Venus in Fur