Arrive on time to see heavenly body (5)
I believe the answer is:
comet
'heavenly body' is the definition.
(comet is a kind of heavenly body)
'arrive on time' is the wordplay.
'arrive' becomes 'come' (coming is a kind of arriving).
'on' is a charade indicator (letters next to each other).
'time' becomes 't'.
'come'+'t'='COMET'
'to see' acts as a link.
(Other definitions for comet that I've seen before include "astronomical sight" , "Small celestial body" , "Tailed heavenly body" , "Celestial object" , "Heavenly body with a fiery tail" .)