departure time vs time of departure

departure time and time of departure both are nouns.

Word	Noun	Adjective	Verb	Adverb
departure time	Yes	No	No	No
time of departure	Yes	No	No	No

As nouns, departure time and time of departure are synonyms defined as:

departure time and time of departure: the time at which a public conveyance is scheduled to depart from a given point of origin

departure time (noun)	time of departure (noun)
the time at which a public conveyance is scheduled to depart from a given point of origin	the time at which a public conveyance is scheduled to depart from a given point of origin