**The same departure window can be the most attractive one for several competing airlines.** Passenger demand and connecting flights often concentrate into particular hours, so each airline has a reason to serve those hours.

Your Los Angeles–Melbourne example illustrates the main factors:

- **Time zones and arrival time.** With a flight lasting roughly 16 hours, an evening departure from Los Angeles produces a morning arrival in Melbourne. That lets passengers spend the day at their destination or continue on a domestic flight. Moving the departure several hours changes that arrival convenience too.
- **Connections at both ends.** An evening departure allows passengers from across North America to reach LAX during the day. A morning arrival offers onward connections in Australia. Qantas explicitly describes its North American schedules as supporting connections and business travel. ([Qantas network guide](https://www.qantas.com/content/dam/qac/network-flyers/North_America_0418.pdf))

Those are likely explanations for the clustering you observed; establishing why each airline chose its exact departure minute would require its internal scheduling decisions.

**Competition itself also encourages similar times.** Suppose most customers want an early flight so they can attend a morning meeting. Both airlines benefit from offering that departure. An airline that moves to midday may gain customers who prefer midday, but lose a larger group to its competitor. This applies particularly to regional and domestic routes with morning and late-afternoon demand peaks. Aircraft availability, turnaround times and airport slots then narrow the choices further. ([MIT’s airline scheduling lecture](https://www.ocw.mit.edu/courses/16-75j-airline-management-spring-2006/a28aa07c64a983ce2cd475b9f7e32f16_lect5.pdf))

Your point about empty seats is reasonable, but **a flight can earn money with some seats empty**. Profit depends on fares collected, operating costs and cargo revenue. Passengers also arrive through each airline’s own connecting network, so two aircraft on LAX–Melbourne may be carrying people whose complete journeys start and end in many different cities. Airlines evaluate that wider network when assigning aircraft and schedules. ([MIT](https://www.ocw.mit.edu/courses/16-75j-airline-management-spring-2006/a28aa07c64a983ce2cd475b9f7e32f16_lect5.pdf), [Qantas international results](https://investor.qantas.com/DownloadFile.axd?file=%2FReport%2FComNews%2F20250227%2F02918373.pdf))

Spreading departures throughout the day would give travelers more choice of times. Each competing airline, however, has a strong incentive to offer the time that attracts the most valuable traffic.