I have a Superb bought new in October 2017 and the time has come when I really should update the maps in the satnav. I have understood the instructions on how to do that, but my question is how long  it takes to transfer the data from, say, a Class X SD card to the system. I have seen references to up to 8 hours, but I expect that that is pretty extreme. What can I expect in practice?

Did mine in about 35 minutes from an SSD drive in a USB caddy.

Updating in the car talks about 30 minutes, getting the download takes me up to 9 hours !!!

The update in the car will resume from wherever it had reached if you dont complete in one journey.

Yes every map update that I have done so far has taken a similar amount of time.