If it's an animation then it doesn't take too long for me. I found that over time I can pretty much automate parts of the process by creating templates for intro / outtro in AE, In Premiere I can drop new shots into a duplicate of the previous sequence which has all the desired effects.
For video (usually travel vlogs), this can run over multiple evenings as I like to get it all just right. There was one sequence within an edit that took me about 4 days to finish - but I did have to change the music and then resync. Getting everything in sync and then adding effects, then getting opinions and tweaking can take time, but these aren't usually small bursts. Editing takes a long time.
I'm assuming the longer videos on youtube take less time to edit? I could be completely wrong. I see many gaming vids that never cut, so apart from an intro/outtro, it's mostly just deciding where to begin and end? That whole vid in itself would probably still take a long time to make though, but could be done in one (long) session.