ありがとうございます！なかなか前置詞の使い方はノンネイティブには難しいですね。 thank you for teaching in detail !

同じです。"A couple of hours" vs "a couple hours of" are two informal ways of saying the same thing. You could even say "I need a couple hours rest" (leaving "of" out altogether) or if you want to be a little more formal, "I need a couple of hours of rest." The word "of" has the same function as の in Japanese.

thank you for helpful advice!!

Dear Ken, From what I know, we use "a couple of" which means several. I need a couple of hours' rest. Hope this helps. Cheers, Lance