question time vs period of time

question time and period of time both are nouns.

Word	Noun	Adjective	Verb	Adverb
question time	Yes	No	No	No
period of time	Yes	No	No	No

As nouns, period of time is a hypernym of question time; that is, period of time is a word with a broader meaning than question time:

question time: a period during a parliamentary session when members of British Parliament may ask questions of the ministers
period of time: an amount of time

Other hypernyms of question time include period, time period.

question time (noun)	period of time (noun)
a period during a parliamentary session when members of British Parliament may ask questions of the ministers	an amount of time