Daily Chinese Idiom Guessing Game
A short period of time; overnight (often used in negative constructions to indicate that something cannot be accomplished quickly).
朝早晨；夕晚上。一个早晨或一个晚上。形容很短的时间。
《周易·坤》臣弑其君，子弑其父，非一朝一夕之故，其所由来者渐矣。”
It takes time to learn a language; it cannot be mastered in a day.