Estimate the duration of an air trip.
Flight time is distance divided by ground speed, and ground speed is where most estimates go wrong. An aircraft cruising at 520 mph through a 40 mph headwind covers only 480 mph over the ground, which is why the same route is routinely an hour longer westbound than eastbound across the Atlantic. Two fixed additions then apply per leg: roughly 35 minutes of taxi, climb and descent that is unrelated to distance, plus your layover time. That per-leg overhead is why two short hops take considerably longer than one direct flight of the same total distance.
Ground speed
Ground speed = cruise speed - headwind (a tailwind adds)
Total time
Total = distance / ground speed + legs x 35 min overhead + stops x layover
The jet stream. At cruise altitude in the northern hemisphere it flows west to east at 100 mph or more, so an eastbound aircraft rides it as a tailwind and a westbound one fights it. On transatlantic routes this routinely makes an hour or more of difference on identical distances.
Taxi out, takeoff, climb to cruise, then descent, approach and taxi in — all of which take roughly the same time whether the flight is 300 or 3000 miles. It is why short hops are so inefficient and why a connection costs you far more than just the layover.