Depends.
If PH, my average would be 7 hours, maybe 6 tops. I memorized the game so much I can rush through it nonstop. Though It won't be a 100 percent run through. If it is a hundred percent, maybe two to five days. Because of the fishing and finding all pieces of ship parts
If ST, 17 hours to complete it. I had a hard time with those Dark trains roaming the tracks, That kept me on edge and excited so much I tend to dilly-dally.
If a 100 percent game, a week.