Delivery will depend on what model you ordered, wheels, battery size, color, your location, and how perfect it comes off the line.
If remedial work is needed to pass inspection, it could be delayed.
If Tesla cannot send a full truck or rail to your location it may be delayed.
If the weather impedes delivery, it may be delayed.
Your delivery specialist will track these items and more, and will have a better ETA as your car works itself through the system.
Just as you are eager to get delivery this year, Tesla will also be eager to get it to you before the end of the year to have it count in this years financials.