long time vs year dot

long time and year dot both are nouns.

Word	Noun	Adjective	Verb	Adverb
long time	Yes	No	No	No
year dot	Yes	No	No	No

As nouns, year dot is a hyponym of long time; that is, year dot is a word with a more specific, narrower meaning than long time:

Other hyponyms of long time include month of Sundays, aeon, eon, blue moon.

long time (noun)	year dot (noun)
a prolonged period of time	as long ago as anyone can remember