Deer come out at dawn and dusk. They are well camoflouged. At dusk, even at 50 yards, you might be hard pressed to see a deer standing still in the open with your bare eyes. Decent binoculars will help you see them better and extend your available hunting hours.
If you cant clearly see a deer at 50 yards in a wide open field with your bare eyes, you should be on your way back to your vehicle and not shooting.
And there is no extending your hunting hours. They are what they are.