Before the ‘-에’ comes a word indicating time, and that comes a noun that indicates a frequency of an action or unit of calculation. ‘-쯤’ carries the meaning of ‘roughly’ or ‘approximately’.
● 하루에 네 시간쯤 한국어를 공부해요. (I study Korean for about 4 hours a day.)
● 하루에 두 잔쯤 커피를 마셔요. (I drink about 2 cups of coffee a day.)