expression
day and night; turning night into day
Set phrase meaning to work or do something continuously without regard for day or night, often implying intense effort or urgency.
彼らは夜を日に継いで工事を進めた。
They carried on the construction day and night.
試験前は夜を日に継いで勉強した。
Before the exam, I studied day and night.
More formal four-character compound with similar meaning; 夜を日に継いで is a more colloquial, vivid expression.
Literally 'continuing night into day'; a fixed idiomatic expression. The exact origin is uncertain, but it has been used since at least the Edo period.