What is Afternoon?

Legal Definition
Afternoon is the time of the day between noon and evening. It is the time when the sun is descending from its zenith in the sky to somewhat before its terminus at the horizon in the west direction. In human life, it occupies roughly the latter half of the standard work and school day. It is also associated with a number of concerns related to health, safety, and economic productivity: generally, the early afternoon, after most people have eaten lunch, corresponds to decreased work performance, decreased alertness, and a higher incidence of motor vehicle accidents. It is usually from 12 PM to 6 PM, but in some countries it may be from 12 PM to 8 PM.
-- Wikipedia
Legal Definition
This word has two senses. It may mean the whole time from noon to midnight; or it may mean the earlier part of that time, as distinguished from the evening. When used in a statute its meaning must be determined by the context and the circumstances of the subject-matter. Reg. v. Knapp, 2 El. & Bl. 451.
-- Black's Law Dictionary