Plane’s instrument’s date shown during change (9)
I believe the answer is:
altimeter
'plane's instrument's' is the definition.
(an altimeter measures altitude)
'date shown during change' is the wordplay.
'date' becomes 'time' (period of time).
'shown during' indicates putting letters inside.
'change' becomes 'alter' (synonyms).
'time' going within 'alter' is 'ALTIMETER'.
(Other definitions for altimeter that I've seen before include "It measures height above sea level" , "Instrument that measures the height above ground" , "Flyer's instrument" , "Aircraft height indicator" , "Plane's height measurer" .)