'RouteFinder' does not require separate integrations and is available by default in Leon.
'RouteFinder' calculates the flight times based on the routing.
In order to have the option available, the Include Route Finder time hint checkbox needs to be activated in the Flight editing section.
The flight time is calculated automatically and the dropdown suggests the block time value. It is based on the flight time calculation from the RouteFinder plus the taxi times from the Airport Directory.