Are you sure in game playtrough time counter includes the time between reloads after dying? It took me 3 day to beat the campaign and I were a bit surprised when it said 8 hours (veteran, killing everyone silently and just being sneaky). Or maybe I was so amazed by the game that I lost track of time.

yeah my game says 7h but when I look at the "longest life" part it still says 7h and I died quite a bit
anyway I don't stealth around a lot, went more with the guns blazing aproach on normal (soldier or whatever it is)