Only half of stores getting prompt delivery (6)
I believe the answer is:
rescue
'delivery' is the definition.
(I know that delivery can be written as rescue)
'only half of stores getting prompt' is the wordplay.
'only half of' indicates taking half.
'getting' is a charade indicator (letters next to each other).
'prompt' becomes 'cue' (cue can mean a prompt or signal).
'stores' with half the letters taken is 'res'.
'res'+'cue'='RESCUE'
(Other definitions for rescue that I've seen before include "Free from danger or captivity" , "Salvage" , "Save from harm" , "Free someone from trouble" , "Extricate" .)