Nightlife mostly turns into a type of entertainment for high flyers (2-6)
I believe the answer is:
in-flight
'a type of entertainment for high flyers' is the definition.
'nightlife mostly turns' is the wordplay.
'mostly' means to remove the last letter.
'turns' indicates an anagram.
'nightlife' with its final letter taken off is 'nightlif'.
'nightlif' anagrammed gives 'IN-FLIGHT'.
'into' is the link.
(Other definitions for in-flight that I've seen before include "On the wing" , "During air journey" , "Provided during plane journey" , "Like airline service" , "taking up?" .)