An airport hotel shuttle appears to run on a simple clock, but the schedule is built around when aircraft arrive and leave in clusters. Everything else about the service follows from those peaks.
Banks concentrate passengers into short windows
Hub airports group arrivals and departures into banks so connections can be made. That means passengers do not trickle out of the terminal evenly across the day.
A hotel shuttle therefore faces a curb that is nearly empty for stretches and then produces thirty people with bags inside ten minutes.
Sizing the vehicle for the average would strand people at every peak, so operators size closer to the peak and accept low utilization in between.
The loop time sets the promised frequency
A shuttle's cycle is the sum of the run to the terminal, the crawl along the arrivals curb, the run back and the dwell at the hotel entrance. Curb time is the least predictable piece.
Frequency is that cycle divided by the number of vehicles in service. A hotel promising service every twenty minutes has committed to enough vehicles to cover the loop at its slowest.
Adding a second hotel to the same loop, common where a group operates several properties on one road, lengthens the cycle and pushes frequency down for everyone on it.
Pickup rules exist because curbs are regulated
Airports assign shared shuttles to designated islands or lots rather than letting them stop anywhere on the arrivals level. Space at the curb is scarce and controlled.
Many larger airports move courtesy vehicles to a common ground transportation center, which adds a walk or a train ride between baggage claim and the pickup point.
That transfer is the part travelers underestimate, and it is why a hotel described as five minutes away can take forty minutes door to door.
Overnight service is the real differentiator
Red-eye arrivals and pre-dawn departures fall outside the hours when a loop is worth running continuously, so many operators shift to on-request service.
On-request means calling on arrival and waiting for a single vehicle to be dispatched, which changes the planning assumption from a headway to an unknown wait.
Confirming the actual hours of continuous service, rather than the existence of a shuttle, is the difference between a plan and a hope on an early flight.
Why the return trip is scheduled differently
Outbound passengers have deadlines, so departure-side service is usually built around fixed times rather than a rolling loop. The hotel wants people grouped into a single run.
A sign-up sheet or a desk-assigned departure slot is a capacity tool. It converts unpredictable individual departures into countable loads.
The consequence is that morning departures fill first, and a traveler who waits until the night before to reserve a seat may be pushed to an earlier run than intended.