Cool. It should come in at a decent length then.
If you doing it in hard mode then it should last about 10 hours (maybe a little less, my Son did it 9 hours but it took me 10:15).
But after you done with it Crushing mode is totally worth another go.In crushing mode it took me almost 12 hours to complete. The AI ismuch smarter and forces you to completely change your play style. No way you can stay in cover for more than a few seconds. Crushing mode is frustrating some times, enfuriating other times and massive fun all the time :)
PS: I got all the 1000 medals and both Cartoon Drake and Doughnut Drake are hilarious to play with ;)