Being observant, but not in the middle of the night! (6)
I believe the answer is:
noting
'being observant but' is the definition.
I can't tell whether this defines the answer.
'not in the middle of the night' is the wordplay.
'the middle of' means to look at the middle letters.
The middle letter of 'night' is 'g'.
'not'+'in'+'g'='NOTING'
Can you help me to learn more?
(Other definitions for noting that I've seen before include "Observing or taking down" , "Recording in writing" , "Paying close attention to something" , "Making brief record as memory aid" , "Making brief record of something" .)