TrueAchievements says 15-20 hrs. It took me 25 to get them all. HLTB agrees with this time for completionist.

Me too! I also highly recommend:

Gone Home - explore your old home to learn everyone’s secrets

It’s because people can’t read it as fast as people talk. Or, the dub has to match up the mouth movements, but the subtitles don’t.

I watched a fan-subtitled anime a long time ago, where they literally translated every word. It was like a paragraph of text on each screen, and it was impossible to keep up with.