I now have the installation instructions. Some points:
Instructions are only valid for cars from radio level 2 onwards.
Retrofit kit No. 65 41 0 443 678 USB/audio interface retrofit kit
65 41 0 445 465 USB/audio interface retrofit kit
The installation time for cars with SA 644 is approx. 2.0 hours, and approx. 2.25 hours for cars with SA 640.
The installation time will be approx. 2.5 hours for cars without SA 640 or SA 644. This may vary depending on the condition of the car and the equipment in it.
Coding is required unfortunately and the kit includes rather more parts than I listed previously, including a retrofit cable that runs from the trunk to the radio and to the USB hub in the footwell.
I am actually surprised that BMW quote such a short installation time.
It is not yet clear to me what second kit number is for as I cannot find it in the ETK. It seems that the 1 series uses the same kit as the 3.