In talking to different dealers when I was in the process of ordering mine, I found that it depended on the dealer and the number of cars they sold / had sold. At one dealer (largest in Canada), they told me in April, that if I ordered then, it would be a July build. The dealer where I ordered is a smaller dealer. I talked to them in May and they had one allotment slot left for an S in June. That's where I ended up ordering mine.
Dealers (at least here in Canada) only know in which month a particular car will be built. They have to wait until they get a VIN from Porsche. That means the car is going into production. My dealer was only able to let me know when the car finished production, when it was shipped to Emden and when it was loaded / shipped from Emden after the car had passed each check point.
Once your car is loaded on a ship, your dealer should be able to give you the name of the ship so you can track it on marinetraffic.com .