time to come vs offing

time to come and offing both are nouns.

Word	Noun	Adjective	Verb	Adverb
time to come	Yes	No	No	No
offing	Yes	No	No	No

As nouns, offing is a hyponym of time to come; that is, offing is a word with a more specific, narrower meaning than time to come:

Other hyponyms of time to come include kingdom come, by-and-by, tomorrow, manana.

time to come (noun)	offing (noun)
the time yet to come	the part of the sea that can be seen from the shore and is beyond the anchoring area
	the near or foreseeable future