work shift vs duty period

work shift and duty period both are nouns.

Word	Noun	Adjective	Verb	Adverb
work shift	Yes	No	No	No
duty period	Yes	No	No	No

As nouns, work shift and duty period are synonyms defined as:

work shift and duty period: the time period during which you are at work

Other synonyms of work shift include shift.

work shift (noun)	duty period (noun)
the time period during which you are at work	the time period during which you are at work