wee small hours
noun [ plural ] uk/ˌwiː ˌsmɔːl ˈaʊəz/ us/ˌwiː ˌsmɑːl ˈaʊrz/ (also small hours, early hours); (US also wee hours)
凌晨
the early hours of the morning, between twelve o'clock at night and the time when the sun rises
There's nothing worse than being wide awake in the wee small hours. 凌晨了还醒着睡不着，没有什么比这更糟糕。