It's a tough call to say when to slit or not. There's no formula saying if the egg is in x situation than cut/don't cut. If I were you I would give them more time. I have had eggs hatch quite a while after sweating, and I've had them hatch after not sweating at all. I think cutting an egg is more of a last resort. I've cut some out before that are still alive now, and I've cut some out that I may have killed. Now, I will only cut to help one out that has already pipped on its own, and is just stuck with a tough piece of egg shell. My philosophy is if they can't make it out on their own, they are weaklings and probably won't make it anyway.