I mean, yes, if you're wearing a watch, it's obviously because you want to be able to tell the time with a simple glance at your wrist, rather than having to pull your phone out of your pocket.
Plus watches are waterproof, and you can bring them with you while swimming/snorkeling/diving/saunaing/whatever, which you wouldn't do with a phone.
Sure, but I feel you are rather unlikely to need to change time zone while snorkelling (unless you snorkel really far!). I understand the point of watches, just not why you would care about the lack of hack for changing the hour.
You missed the point; you aren't changing time zones while snorkeling, but you are still wearing the watch. The point is you don't have your phone with you while snorkeling so you have to check the time on your watch, and because you're traveling, you had to change the time when you got there, which the independently adjustable hour hand made easier.
An independently adjustable hour hand is a useful complication on a watch for traveling across time zones.
Plus watches are waterproof, and you can bring them with you while swimming/snorkeling/diving/saunaing/whatever, which you wouldn't do with a phone.