Eric, I have ordered several MB & BMW from factory before. If you start from a clean slate - 90-120 days to arrive at Long Beach ( I am from California.) Perhaps a bit sooner if you are from the east coast.
Sometimes you can get ordered cars faster if that car is already in the pipeline and your dealer gets in the window when one can still change the options to your specifications.
The dealers may have some cars in by September, but they are certainly not cars that you order now. There is simply not enough time. You, may, however, find a car equipped close to what you want.
AMG is a whole different story. Mercedes Benz is going to make 10000 CLA45 AMG for the world market in 2014 ( according to press release ) and most are coming to the United States. I am guessing
7 out of 10. So there are 7000 CLA45 destined for US. That's less than 600 a month. Total US Mercedes dealership numbers somewhere around 300-350. So, on average, 2 CLA45 per dealership per month.
"AMG Centers" may get more cars, so smaller dealership may end up getting just 1 a month. I am calling my sales rep weekly to make sure they don't leapfrog my spot (#2) for special "friends of the general manager" but that will happen for hot cars like my M3 when it was first introduced and the C63 in 2008. I bought two cars from my MB dealership this past 5 years and have my cars serviced there. But that just makes me one of many, many...