air alert vs time period

air alert and time period both are nouns.

Word	Noun	Adjective	Verb	Adverb
air alert	Yes	No	No	No
time period	Yes	No	No	No

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

air alert: the time period during which military and civilian agencies are prepared for an enemy air attack
time period: an amount of time

Other hypernyms of air alert include period, period of time.

air alert (noun)	time period (noun)
the warning signal that begins a period of preparation for an enemy air attack	an amount of time
the condition in which combat aircraft are airborne and ready for an operation
the time period during which military and civilian agencies are prepared for an enemy air attack