The part of the day, mostly at night, when someone has the habit and/or desire of masturbating.
9gagger: BOOBIES!!! I see its Fap O' Clock!
by rub'o'cloker August 18, 2012
The time of night where a male cannot sleep until he masturbates. This time will last until he successfully masturbates.
"Man, I've been lying in bed for hours and still can't sleep, must be fap o'clock"
by Reptilious July 01, 2012