Tesla employees have the delivery date, Oct 17'- Dec 17'. They are being invited to configure their car now. Tesla employees are most likely urged/forced to not release any information about the Model 3 until regular consumers can recieve the same information.
The next batch of deliveries will be the consumer. The earliest delivery date will be Nov 17'- Jan 18'. I suspect they will configure their car next month (Late August, early September). Tesla probably expects all the beans to be spilt by this group. (Aka all specs and every nook and cranny within the Model 3 to be revealed)
After those deliveries, the next batch of consumers will configure their car. The Dec 17'- Feb 18'. Like I said, I suspect the configuration of the car to be a month after the previous consumers. (Late September, early October).
I don't think there is a simple answer to this question, because Tesla will not have scaled to 5,000 cars produced per week until then end of December. To that end there is likely some variability between when you confirm and when you get the car. I'm in the November - January group that @Kriffic mentioned above so I won't delay for a second in hopes that I can hit in 2017.