There's another reason why you shouldn't rush in - the lil chick is absorbing nutrients all the time from the sack that's attached to the shell and if you break that inadvertently it can bleed and die. Keep the shell ever so slightly damp by flicking water on it (be careful not to drown chick!) or laying a warm damp paper towel on it for a few seconds. It's very hard to stand by and watch them struggle but sometimes it does take 24hrs plus. Some folk do say that you can VERY carefully remove just a tiny bit of shell. Fortunately I haven't had to ever intervene.
We too have some eggs that I thought were in the hatching process under a Muscovy but I notice today that she's off the nest and hasn't carefully covered them up before getting her snack. They are quite cold to the touch so sadly she's maybe given up half-way through