You can either explore everything in the first playthrough, and maybe do a shorter 2nd one, or do several shorter playthroughs to discover what you missed before. From what you wrote, you're closer to the 1st type.For me a play duration is just too long, I don't have the exact time because I certainly let the game open without playing many time. But it's very long. Let be clear each time I find my courage to play it again I end enjoy and play for too long time for the session, but still it's too long.
I've done the same and I agree that it can be very long. I've played about 300 hours without counting the EA, but the saved file shows 194 hour, so there were a few reloads to explore other options and so on. I bet @Pladio will have less than half this duration. I was surprised at the difference between several players, but that means this game can potentially keep you busy for a very long time if you don't go forward with the story.