Hop on a Gryphon, Wyvern or whatever your local flight master offers and this mod will show you a DBM timer for the remaining time.
Currently only supports "standard" flights, no weird Quest-related flights at the moment. This means that this works best in Classic and WotLK, Retail players may want to prefer InFlight Taxi Timer for a more complete coverage.
We currently just take the timers from InFlight that are crowdsourced on WoWInterface, we currently do not maintain our own database for flights.