Just finished Bowser's Fury with 50 cat shines obtained. When you go back to the game, more stuff opens up and there's 100 shines total you can get.
Unless I missed something, there's no stats, so not sure how much time I played today, but am guessing it was around six hours total? If you want everything, I'm thinking it's going to be around 10-12 hours total. Could be less because you can start warping around once you clear the game once.
Having a Bowser amiibo (I have cheapo bootleg amiibo card) also helps a lot. It will summon Bowser and you'll need him since his presence means blocks pop up that normally aren't there and/or he can destroy certain blocks for you. Otherwise you have to wait for him. I think that was kind of dumb and there should be a way to summon him in-game without the amiibo.