One crazy time! (3)
I believe the answer is:
eon
'time' is the definition.
(I've seen this before)
'one crazy' is the wordplay.
'crazy' indicates anagramming the letters.
'one' anagrammed gives 'EON'.
(Other definitions for eon that I've seen before include "Era" , "plenty of time" , "Huge time period" , "Geological period" , "thousand million years" .)