There is no specific or definitive time that afternoon becomes evening, but it gradually shifts into evening as the day goes on. It is unlike afternoon, which begins after 12 p.m.
Evening is defined as the later part of the day in between afternoon and nighttime. It is generally not light out when evening starts, but the day will gradually fade into darkness as evening carries on.
In the Southern part of the United States, evening is generally used to define the time between when the last meal of the day is eaten and when a person goes to bed. Evening can also be defined as the period of time between sunset and when a person lays down for the night.
The word evening comes from a Middle English word that literally means the day turning into night. It was used before the 12th century and was used to describe any time of the day when the person using it believed that it was turning to darkness. The word also has origins in the Greek language from the word 'epi.' 'Aband' is a German word that means the afternoon turning into night; 'evening' could have possibly come from that word.