About time to adjust the height indicator (9)
I believe the answer is:
altimeter
'the height indicator' is the definition.
(I've seen this before)
'about time to adjust' is the wordplay.
'about' means one lot of letters goes inside another.
'to adjust' becomes 'alter' (I've seen this before**).
'time' going into 'alter' is 'ALTIMETER'.
(Other definitions for altimeter that I've seen before include "Instrument to measure height above ground" , "Height gauge" , "It measures height above sea level" , "Aircraft height indicator" , "something in the cockpit" .)