Fantastically great time for goal (6)
I believe the answer is:
target
'for goal' is the definition.
(target is a kind of goal)
'fantastically great time' is the wordplay.
'fantastically' indicates anagramming the letters (a fantastical ordering of the letters).
'time' becomes 't' (abbreviation).
'great' anagrammed gives 'targe'.
'targe'+'t'='TARGET'
(Other definitions for target that I've seen before include "'Aim, goal (6)'" , "purpose" , "Butt" , "desired objective" , "The object with the bullseye" .)