Middle of day, time to stand still (2,4)
I believe the answer is:
at rest
'still' is the definition.
(synonyms)
'middle of day time to stand' is the wordplay.
'middle of' indicates the central letters.
'time' becomes 't' (abbreviation).
'to stand' becomes 'rest'.
The middle letter of 'day' is 'a'.
'a'+'t'+'rest'='AT REST'
(Other definitions for at rest that I've seen before include "Free from trouble or anxiety" , "Stationary" , "Immobile" , "In relaxed state, perhaps dead" , "Still" .)