The perfect opportunity to poop with little effort. In other words, the body and mind's optimal time to release a demon. Once missed, said demon retreats, solidifies, and cements itself in your lower intestine until the next pooportunity.
Chad:"I had the perfect pooportunity, but I passed it up because I'm too self-conscious to shit in the middle of a parking lot"
Bruce: "Man, you done fucked up. That sweet shit baby demon lives inside you now."
Susan: Oh my god, this staff meeting better end soon or I am going to miss my Window of Pooportunity.
Hannah: Hang in there, Susan, Tom is almost finished.
Susan: I sure hope so...
Steve: Aww shit, I missed my window of pooportunity and now I can't even pinch a pea.
Joe: Shit, man, I hate that. That's why I never schedule anything between 3 and 6 PM.