1
general::
Also, wee hours. The hours following midnight, as in I stayed up working through the small hours, or The parents didn't come home until the wee hours. The adjectives small and wee both refer to the low numbers of those hours (one o'clock, two o'clock, etc.). [c. 1830]
American Heritage Idioms
2
general::
Phrase(s): the small hours (of the night) [and] the wee hours (of the night)
the hours immediately after midnight. • The dance went on into the small hours of the night. • Jim goes to bed in the wee hours and gets up at lunchtime.
McGrawhill's American Idioms And Phrasal Verbs