Nerites are one of those snails that will just keep popping out of the dang water until they get used to it at their own speed lol! Whenever I put some in a new tank, or the water parameters change wildly, etc, the nerites all hop out and hover about the water line until they feel good to ease themselves back in. In fact, I think it's fair to suspect that your water params have gone a little wonky! Lord knows my guys have flagged a few pH swings for me!
I am not sure how long they have been hiding on you for, but it is likely that they are camping out in their shells for a bit until the warm up to the water. Give them a day. Perhaps change the water to alleviate the nitrite situation a bit, but honestly they are slow starters lol. I think they'll be fine in a day or so.