You can anticipate the delivery of the vehicle in September. After your pre-order is complete, MB must establish an order number. The order number will allow the dealership to track the vehicle for you until it arrives at the dealership.
Most dealerships will require a deposit for the pre-order which can range from $500 to $2,000. I placed a pre-order back at the beginning of last month and I still am waiting on an order number to be established. Worst case, if the vehicle doesn't arrive in September I will just get one of the initial vehicles that comes in with their first shipment of vehicles.