party o' clock 

n. That time of night when teenagers and young adults can be expected to arrive at a party.

The expression is used mostly among college-aged adults who typically party-hop or bar-hop on the weekends. The ambiguity of the phrase avoids the potentially embarrassing situation of a guest arriving too early for a party or a host(ess) waiting for guests to arrive. See also party foul.

The term is most often encountered on Internet invitations or mass e-mails advertising a private party.

The time is generally understood to be between 10pm and midnight.

"What time are you heading over to D's house?"

"Party o' clock"

party o' clock by mxm February 9, 2009