hard time vs difficultness

hard time and difficultness both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard time	Yes	No	No	No
difficultness	Yes	No	No	No

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

hard time: a difficulty that can be overcome with effort
difficultness: the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result

Other hypernyms of hard time include difficulty.

hard time (noun)	difficultness (noun)
a difficulty that can be overcome with effort	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result
a term served in a maximum security prison