Reading for one hour having left cast (4)
I believe the answer is:
town
'reading for one' is the definition.
(Reading is a town)
'hour having left cast' is the wordplay.
'hour' becomes 'hr' (abbreviation).
'having left' is a deletion indicator.
'cast' becomes 'thrown' (cast can mean to throw).
'thrown' with 'hr' removed is 'TOWN'.
(Other definitions for town that I've seen before include "more established area with 1a [OLD]" , "It lies between village and city" , "See 1" , "Urban area larger than a village" , "Urban community" .)