Transit
The angle between a planet where it is right now and a point in your natal chart.
The natal chart stays put; the sky keeps moving. A transit is the geometry between the two — Saturn as it is today sitting exactly on your natal Moon, say.
Speed sets the tempo. A Moon transit is over in a couple of hours; a Jupiter transit runs for weeks; a Pluto transit can span two or three years and cross the same point three times because of retrogrades. So "how long does this transit last" ranges from hours to years.
Transits describe timing, not events — which themes get pushed to the surface over a stretch, not what happens on a given date.