Green’s Dictionary of Slang

see under black n.

see under bright n.

(US campus) a party, usu. at a fraternity house, that does not start until after the bars and clubs close.

1985		Eble Campus Sl. Apr. 5: late-night – a party [...] The late-night was so crowded that we didn’t get past the porch.
1996		Eble Sl. and Sociability 57: A late-night is a ‘party, usually at a fraternity house, that does not get started until around one in the morning and usually gets very big’.