We worked well into the small hours.

我们一直工作到了午夜之后。

《牛津词典》

They were arrested in the small hours of Saturday morning.

他们在周六凌晨时分被捕。

《柯林斯英汉双解大词典》

He was so engrossed in his work that he frequently stayed up until the small hours.

他全神贯注地工作，经常工作到下半夜。

《新英汉大辞典》