I have started routes to Europe but I always get the flag that it cannot be flown in one day on one aircraft so I need double the airplanes. Then I have to back and put "stuffers" in the schedule to increase usage. Yet I see so many that routinely fly one day turns to Europe seven days a week. What is the trick? I can't speed up the plane and I cannot reduce ground time.
7-day scheduling is the key. One bigger schedule going 24-7 (except the A-check), but applied or spread over 7 planes.
Tutorial here: https://www.airwaysim.com/forum/index.php/topic,71633.0.html (https://www.airwaysim.com/forum/index.php/topic,71633.0.html)
Look for the picture in the 2nd post, it should clarify your basic understanding of this method. Then read :)