Every square is sixty seconds of the front page — your name, your line, your link, nothing else on the screen. Pick one. Red squares are gone for good. 0 sold on this day so far.
Minutes are priced by when tech X is actually awake. 14:00–18:00 UTC is the overlap between the US morning and the European afternoon, so it costs the most. 03:00 UTC is the cheapest minute of the day, because nobody is looking. The curve moves as the real traffic data comes in.