Girl has half-an-hour in a state (5)
I believe the answer is:
idaho
'in a state' is the definition.
(I've seen this before)
'girl has half-an-hour' is the wordplay.
'girl' becomes 'ida' ().
'has' means one lot of letters go next to another.
'half an' indicates taking half.
'hour' with half the letters taken is 'ho'.
'ida'+'ho'='IDAHO'
(Other definitions for idaho that I've seen before include "North-western US state" , "My Own Private -- (1991 film)" , "The Gem State, known for its potatoes" , "US state S. of Montana" , "US state in the Rocky Mountains" .)