Having us dress when the siren goes off. It’s early (7)
I believe the answer is:
sunrise
'having us dress when' is the definition.
I can't judge whether this defines the answer.
'siren goes off it's early' is the wordplay.
I cannot quite see how this works, but
an anagram of 'siren' is 'nrise' which is located in the answer.
This explanation may well be incorrect...
'the' acts as a link.
Can you help me to learn more?
(Other definitions for sunrise that I've seen before include "Dawning of the day" , "It gets the day off to a bright start" , "The first light of day" , "Time of full daylight" , "everyday occurrence in the East" .)