Time for a different one! (3)
I believe the answer is:
eon
'time' is the definition.
(I know that eon is a type of geologic time)
'different one' is the wordplay.
'different' indicates anagramming the letters (letters placed in a different order).
'one' anagrammed gives 'EON'.
'for a' acts as a link.
(Other definitions for eon that I've seen before include "Very long age" , "Prolonged period" , "Vast period" , "Immense period" , "An immense time" .)