It depends a lot on how efficient their flight is. Birds start out kind of sprinting equivalent a lot of the time when we see them flapping lots but long distances is different . Apparently an albatross can do about 500 miles in a dayHow far do you think large flying creatures should be able to travel in a day? I generally feel 60-70 miles feels too little; something in the 90-200 miles range seems ok to me. My suggestion above that a 5e adult dragon should have a sustained overland flight rate of around 40 mph might indicate more like 320 miles in a day, though.
I guess a flying carpet doing say 20 mph would be maybe 12 hours of flight before it got too uncomfortable (is a carpet better or worse than a car?) would do ca 240 miles/day.
Engineers identify key to albatross' marathon flight: Flying in shallow arcs helps birds stay aloft with less effort
Engineers have developed a new model to simulate dynamic soaring, and have used it to identify the optimal flight pattern that an albatross should take in order to harvest the most wind and energy. They found that as an albatross banks or turns to dive down and soar up, it should do so in...