I was in my settlement farming for some purified water and I went to sleep in one of my settler's beds for a day but when I was sleeping, instead of the usual 24-ish seconds it normally takes it took about 5 minutes and the time was ticking down extremely slowly. I don't know if this is a bug or it changes...?

I experience that all the time. It is quite annoying. Can't be lack of cpu power, because I have more then enough of that. Not sure if the gpu would have something to do with it. Maybe limiting my fps to 30? I noticed it doesn't occur in diamond city.

That's normal, has something to do with the settlers. The more you have the greater the lag.

The game probably has to process what all of your settlers do in those 24 hours and calculate where they are now, has their happiness changed etc

Sounds like there might be an error with the scripts. Some sort of loop that needs to time out, maybe. I'd report this to the tech support staff.

I've never encountered this, myself, and I've had some pretty big settlements.