Note that the speed of a download is dependent on the slowest component in the entire process.
It totally depends on your internet speed and the speed of the server from which you are downloading the update. How long does it take to download Windows 10? I know how frustrating it can be if it takes too long to install and you are staring at a loading icon which doesn't give any information at all.
If you are wondering how long it takes to download and install windows 10, then you have come to the right place! However, I should mention that there is no fixed answer to this question as it depends on a lot of factors like your internet speed, your hard disk speed, your computer configuration and many other variables.