Excitedly eager past midnight? (4)
I believe the answer is:
agog
'excitedly eager' is the definition.
(I've seen this before)
'past midnight?' is the wordplay.
'past' becomes 'ago' (similar in meaning).
'midnight?' becomes 'g' (the middle letter in 'night').
'ago'+'g'='AGOG'
(Other definitions for agog that I've seen before include "Eager and wide-eyed" , "Excitedly eager" , "Very eager (to see or hear something)" , "Full of expectation" , "State of wide-eyed wonder" .)