The idea of putting it back in the middle of day (6)
I believe the answer is:
notion
'the idea' is the definition.
(notion is a kind of idea)
'it back in the middle of day' is the wordplay.
'back' says the letters should be written backwards.
'in the' indicates putting letters inside.
'middle of day' becomes 'noon'.
'it' written backwards gives 'ti'.
'ti' placed inside 'noon' is 'NOTION'.
'of putting' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for notion that I've seen before include "A vague and possibly incorrect opinion" , "Vague understanding" , "Idea, concept" , "Vague idea or opinion" , "Whim or fancy" .)