Windows 10: When and how does the hibernation work?

I have turned on my laptop and it says "Sleep is being prepared" for a little over an hour, how long will it take to get this hibernation ready and what exactly is it doing?

I.d.R. It only takes a few seconds. - The first time maybe a few seconds longer, but not for hours.

If e.g. Your hard drive is almost full, I could imagine that it takes longer. Or the system simply "hung up".

If you send the computer to hibernate rather than shut it down, everything will stay the way you left it the next time you boot up. If you have used the browser, the pages are still there, programs and files are still open and you do not have to open everything again. The whole usually takes less than a minute. I've been using this feature for a long time and only shut down the computer for updates. Otherwise, always idle.