Hustling around in the daytime (8)
I believe the answer is:
sunlight
'the daytime' is the definition.
(thesaurus)
'hustling around' is the wordplay.
'around' indicates an anagram.
'hustling' anagrammed gives 'SUNLIGHT'.
'in' is the link.
(Other definitions for sunlight that I've seen before include "Solar rays" , "Solar illumination" , "Prerequisite for photosynthesis" , "Possible reason why blinking" , "Form of illumination" .)