This phrase is used to substitute a real time when it has become too late at night. Time is unimportant at the moment because of a number of reasons including: having a good time, becoming delirious from major sleep deprivation, too lazy to look at a clock/watch, etc.
Person #1: Whoa! I almost forgot I have to go. What time is it?
Person #2: I don’t know. It’s Late O'clock.
Person #1: Oh well, see you later!
Also known as CPPT, it is a trend when you see one brave friend who decides to change his/her facebook profile picture, so you change your profile picture and eventually about 20 or more friends have all changed their picture because it's contagious.
This trend goes in waves because it's contagious.
One can wonder how contagious this trend is and if the trend really ever ends?
Friend 1 changed their profile picture.
...1 hour later
Friend 1 and five other friends changed their profile picture.
Friend 2: Looks like my friends are going through the contagious profile picture trend.