The gap between a connecting arrival and departure is not chosen by the traveler alone. Each airport publishes a minimum connection time, and booking systems refuse to construct itineraries that fall below it.
The figure is measured, not estimated
Airports and airlines establish minimum connection times based on the actual physical process of moving a passenger and a bag between gates.
The measurement includes taxi time after landing, deplaning, walking distance, any transfer between terminals, and the time required to reach the departure gate before it closes.
Because layouts differ enormously, the same airline can have different minimums at different airports, and a large hub may publish several figures for different terminal pairs.
Different connection types get different numbers
A connection between two flights on the same airline within one terminal carries the shortest minimum, since bags move within a single baggage system.
A transfer between airlines takes longer, because bags may have to pass between separate handling operations and check-in systems.
International-to-domestic connections carry the longest figures in the United States, since arriving passengers clear immigration, reclaim bags, pass customs and re-deposit their luggage before continuing.
Baggage sets the real constraint
A passenger can often run between gates faster than a bag can move through a sorting system, so the published minimum is frequently governed by luggage rather than by people.
This is why a traveler who makes a tight connection sometimes arrives without their bag. The itinerary was legal but the baggage transfer did not complete in time.
Ground handlers prioritize connecting bags with short windows, and many airports maintain a hot transfer process for exactly these cases, which succeeds often but not always.
Legal connections carry protection
An itinerary booked as a single ticket that meets the published minimum is a legal connection, and the airline is responsible for rebooking if the first flight runs late.
Booking two separate tickets removes that protection entirely, regardless of how much time sits between them, because no carrier has agreed to carry the passenger through.
This distinction is the practical reason to prefer a single ticket, and it matters far more than the length of the gap on the schedule.
Padding the gap has limits
Longer connections reduce the chance of misconnecting, but they also lengthen exposure to a delayed inbound aircraft that never arrives at all.
Late-day connections carry more risk than morning ones, since delays accumulate through the operating day and there are fewer remaining flights to rebook onto.
A short morning connection at a familiar hub can therefore be safer in practice than a generous evening one at an airport where the airline operates only a few daily departures.