If you're interested, there is a great thread on this exact topic - 23 pages of everything you'd ever want to know and more. (Search "How to follow a new BMW from Order . . ." and you'll see it).
Mine left Bremerhaven on 10/24 and docked in Baltimore on 11/7. The ships are on a set schedule. Unknown part is time from VPC to your dealer. Depends on if you have any VPC installs (and in rare cases VPC repairs) and then how many cars are going where. Your dealer gets a report every weekday on their inbound inventory, so they should be able get your delivery date to within a few day window.