Nurse is disturbed at dawn (7)
I believe the answer is:
sunrise
'dawn' is the definition.
(synonyms)
'nurse is disturbed' is the wordplay.
'disturbed' is an anagram indicator (the order of letters is disturbed).
'nurse'+'is'='nurseis'
'nurseis' anagrammed gives 'SUNRISE'.
'at' acts as a link.
(Other definitions for sunrise that I've seen before include "The first light of day" , "It's preceded by dawn" , "It gets the day off to a bright start" , "Dawning of the day" , "What follows dawn" .)