lol at 1-4hour repop NM, i am hardcore myself but sorry that is a big no.
longer repop time doesn't equal to challenge, your ability to wait longer than the others doesn't make you a better player.

What needs fixing with NMs are the levelof difficulty, like 4-5x current difficulty.
Make it very hard that unorganized group of players wether it being casuals or hardcore will wipes alot and even very organized group with have a godamn hard time with it, that is where the sense of the accomplishment comes from.