Most of my brides come to me completely unsure of how many hours to book--and that's totally ok! To help them make the decision, I tell them to keep a couple things in mind... 1) 8 hours of coverage is generally what you need to capture everything from the getting ready photos through the sparkler exit. If you want less coverage, that's absolutely fine too--and we would then work together to figure out whether I would be there for getting ready photos or the exit, since I usually couldn't capture both in fewer than 8 hours. (There are always exceptions, but that's usually the case.)
2) Before a bride decides to skip the getting ready shots, I make sure she knows that that's when I capture not only the actual getting ready process, but also all of the detail shots such as the dress hanging up (like the image above), the shoes, the garter, the invitations, the rings, the flowers, etc. So if those photos are important to you, then we would want to make sure your coverage would include that time.