Ten photos developed immediately (2,3,4)
I believe the answer is:
on the spot
'immediately' is the definition.
(thesaurus)
'ten photos developed' is the wordplay.
'developed' is an anagram indicator.
'ten'+'photos'='tenphotos'
'tenphotos' anagrammed gives 'ON-THE-SPOT'.
(Other definitions for on the spot that I've seen before include "Apply ointment here" , "Where snooker ball may be replaced" , "sort of fine" , "At a particular place of action" , "In an awkward predicament" .)