Small number performing in middle of the day (4)
I believe the answer is:
noon
'middle of the day' is the definition.
(I've seen this before)
'small number performing' is the wordplay.
'small number' becomes 'no' (abbreviation for 'number'; 'small' suggests an abbreviation).
'performing' becomes 'on' (as in being on stage).
'no'+'on'='NOON'
'in' is the link.
(Other definitions for noon that I've seen before include "Twelve o'clock, midday" , "High time of day?" , "12 pm" , "when PM starts" , "when only mad dogs go out?" .)