day and night; around the clock
Used adverbially or as a noun to describe something happening continuously, both during the day and at night.
彼は夜昼働いている。
He works day and night.
夜昼
The temperature difference between day and night is extreme.
Compound of 夜 (よる, 'night') and 昼 (ひる, 'day'). The reading is a straightforward combination of the kun'yomi of each kanji.