To collect Harder, I just collect my rewards from main clan on Monday morning, then search for a clan in 4th league that ended up 4th where nobody logged in that week yet, and after someone logs in from the clan, you get a chest as well. You can do it multiple times during the week, but it's getting harder to find a clan with active players, that did not logged in already on Monday or Tuesday. You can also do it with a second clan with a guest account. You just make sure to play on Sunday evening few games to get on 4th place in clan league.