One rather unrealistic assumption in the flight scheduling model is that a given plane can fly two consecutive flights with no downtime. For example, it could fly flight 5903 that gets into...

One rather unrealistic assumption in the flight scheduling model is that a given plane can fly two consecutive flights with no downtime. For example, it could fly flight 5903 that gets into Washington, D.C. at time 14 and then fly flight 7555 that leaves Washington, D.C. at time 14. Modify the model so that there must be at least one hour of downtime between consecutive flights.