I heard my colleague's friend in UK got the similar message about 3-5 months.
When customizing the cars from Land Rover or Jaguar, we got the long wait and delay, too.
My last experience was Porsche Cayenne would arrive in the end Jan/Feb 2018 if I order it before the end of September in New York.
This is why those dealers always ask us to pick up the cars from their lots if you don't want to wait and you like to get better price.
Anyway, from the car was ordered to arrived, my x35i was about 20-days (8-days production) and my 40e was about 24-days (12-days production). As jlstyle mentioned, 3-5 weeks would be very common over here as long as BMW plant has everything your car needs.
And the schedule and status of the cargo ship could also be the big factor.