It depends on the speed of your wifi and the speed of the internet connection.
Internet recovery will download about 600MB-1GB for the initial installer operating system. When you start installing it will also download the OS installer files that are around 6GB.
All of that can take a long time if the internet or wifi is slow (I have heard tales of 12 hours and longer).
If you have another Mac it is far better to download the installer & make a USB installer less things can time out or fail. It can be quicker if the wifi & internet connection are stable.