Venture for half days (5)
I believe the answer is:
foray
'venture' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'for half days' is the wordplay.
'half days' becomes 'ay' (I am not sure about this - if you are sure you should believe this answer much more).
'for'+'ay'='FORAY'
Can you help me to learn more?
(Other definitions for foray that I've seen before include "Assault" , "Raid or incursion" , "Depredation" , "Brief incursion" , "Brief attack" .)