Internet recovery on imac

Sometimes a large download of an operating system can take up to an hour depending on various factors. Then it takes more time to install (can be 45 minutes or so), so be patient. I have one very strong suggestion. If at all possible, do not use wi-fi. It's too much data for wi-fi and it often get corrupted. If you can, have your computer directly connected to your modem/router via a USB cable. If you can not, then I would temporarily move the computer. Failing that, you may have to do several downloads via wi-fi before you get a clean one that successfully installs. Good luck to you.

It depends mostly on the speed of your internet connection.