How long can it take to transfer your data from one phone to a new one

There is not a set length of time, as it depends on the speed of your WiFi connection and the size of the backup/data being transferred.

Make sure you have a good internet connection, you may want to stay close to the router to ensure it is as fast as possible.

Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch

That depends on how much data and how you are transferring it.