2. A window of opportunity from early a.m. until usually about noon or 1 p.m., in which drinking caffeine is ok. For the recovering caffeine addict who can no longer drink caffeine after mid-morning or early afternoon, lest he be force into some sort of crazy all-nighter bullshit, in which he's either up all night unable to sleep or simply brewing pot after pot in order to generate an next morning mania for work.
Dude 1: I can't have coffee at night anymore.
Dude 2: Oh? Why's that?
Dude 1: Waaaay too late. I'm outside today's caffeine window.
Dude 2: Ha! Whatever...
Dude 1 goes and gets a coffee anyway.