re " At break of day " and the Bizet tune and Singing Together.
It seems to be an 18thC French song attributed to Joseph Domergue  
with various translations.
Even different versions in French  


Someone has written about it here oldfatherchristmas

Well there are many threads on Singing together .,.. mudcat.might be worth checking if anyone might have a paper copy?

Other links
French
French YouTube