lights-out vs bedtime

lights-out and bedtime both are nouns.

Word	Noun	Adjective	Verb	Adverb
lights-out	Yes	No	No	No
bedtime	Yes	No	No	No

As nouns, bedtime is a hypernym of lights-out; that is, bedtime is a word with a broader meaning than lights-out:

lights-out (noun)	bedtime (noun)
(military) signal to turn the lights out	the time you go to bed
a prescribed bedtime