day and night; around the clock
Used adverbially or as a noun to describe something happening continuously, both during the day and at night.
He works day and night.
夜昼の寒暖差が激しい。
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.