A number needing a nap at mid-morning (5)
I believe the answer is:
dozen
'a number' is the definition.
(dozen is a kind of whole number)
'a nap at mid-morning' is the wordplay.
'a nap' becomes 'doze' (I've seen this before).
'at' says to put letters next to each other.
'mid' says to take the centre (mid- can mean the middle of something).
The middle of 'morning' is 'n'.
'doze'+'n'='DOZEN'
'needing' acts as a link.
(Other definitions for dozen that I've seen before include "Twelfth of a gross" , "See 4" , "Group of 12" , "XII" , "Quantity of e.g. eggs" .)