A question I get a lot of how long of a session you should book... there's a few things to consider when booking any photography session but especially a family photoshoot!
How long of an attention span does my family have? When working with younger kids, sometimes they only last 10-20 minutes. If that's the case, looking at a mini session might be best! If they have a longer attention span, you want photos of them just being candid or if you want photos without them in it, you can look at a longer session than a mini session. On the flip side, if working with a newborn, it's best to schedule at least an hour so you can plan for tears, feedings, diaper changes, etc.
How many outfits/location do we want? If you're only needed one outfit at one location, family photos can fly by quickly! Traveling and changing outfits takes more time than taking a photo so take that into account when planning for family photos.
What do I want out of these photos? If you're just wanting a few updated photos of your immediate family, a full hour or longer probably isn't necessary. If you're wanting a large variety of photos, poses, groupings of a larger family while using props, you probably want to look at more than a mini session.
There are obviously more factors to keep in mind, but in my many years of taking family photos, these seem to be the biggest players in how long of a shoot you should book!