This doesn't work on Warmane. Some time ago an attempt to enable it caused issues with shared IDs and so they reverted it back to its early WotLK state.
You will queue for RDFs randomly, only getting HCs which you haven't done for the day. When you've done them all (which means you already played some 4-5 hours, jeez, go out, get some friends), you can go do the Sons of Hodir dailies, grind professions or do PvP (but seriously, just get a life instead - this comes from a guy who used to play WoW 12h/day).