canonical hour vs time of day

canonical hour and time of day both are nouns.

Word	Noun	Adjective	Verb	Adverb
canonical hour	Yes	No	No	No
time of day	Yes	No	No	No

As nouns, time of day is a hypernym of canonical hour; that is, time of day is a word with a broader meaning than canonical hour:

canonical hour: (Roman Catholic Church) one of seven specified times for prayer
time of day: clock time

Other hypernyms of canonical hour include hour.

canonical hour (noun)	time of day (noun)
(Roman Catholic Church) one of seven specified times for prayer	clock time