duty period vs work shift

duty period and work shift both are nouns.

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

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

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

Other synonyms of duty period include shift.

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