what is your rifle zeroed at? did you shoot over them?. probably so.
which state you hunting? Southeast US sunset times are at about 5:30 pm , right around there. The further north you go sunset times will change. will be earlier. Today at NYC sunset was 4:58 but in Savannah, Ga sunset was at 5:28 . and they are in the same time zone.
ANyways with good quality glass in a 50 mm optic, you can safely and ethically hunt right up to legal shooting times. ( where i hunt , it is 30 minutes after sunset)
I would suspect that you will need to hold under at closer ranges.
American by birth, Southern by the grace of God.