There is no precise definition of late afternoon, except that it is the part of the day that is just before evening time. Oxford Dictionaries defines afternoon as the time between noon or lunchtime until evening.
Cambridge Dictionaries Online states that afternoon is from about noon or after the midday meal until about 6 p.m. or when the sun begins to go down. In Middle English, the word for afternoon was "aftermete," which means "after the noon meal." Given the variations in mealtimes and the times of sunset, the period of late afternoon is difficult to define. The term "late afternoon" can sometimes substitute for the word "evening."