I like what Hitched said in their article "Weddings can be seriously long and your photographer is only human. It’s a huge ask to suggest they work from when you get your hair done at 7am to the last dance at midnight." it made me chuckle because it's true but of course, it's so easy to get wrapped up in the joy of the day and so you don't want to leave. I recently stayed at a wedding 2hrs past the agreed time because the dance floor was so amazing for photos haha! However yes, usually photographers will have packages of hours for the day. It very much depends on what time your ceremony is and how long you'd like the photographer there for the getting ready part of the day as to what number of hours you need.
Most of us can cover shorter days out of season, and then in wedding season it's usually 8hr, 10hrs, or 12hrs. That's how mine are structured anyway. I've only done 2 weddings this year that are 12hrs long and it took me two days to recover lol
So most of the time my packages will be 8 hours to 10 hours, which is generally enough time to cover from prep to just after the first dance and a bit into the party. However I don't clock watch so if something is happening then I stay to capture it!