Time ostenibly spent in the bathroom (derivative of "to flex" = Pooping) but more to the point spent at other pursuits - video solitare, reading the newspaper, collecting your thoughts, jerking off, or all of the above - while in the stall and/or bathroom. Occurs daily worldwide.
Dave stood, grabbed the crossword puzzle and headed for the bathroom. "I'm going to take some flex time," he announced
when a male takes a dump into a condom, then using the condom as a dildo to his partner. the condom then breaks, resulting in "explosion" of the indian time bomb