Set about a dozen eggs last thursday, silkie and orps. have tried candling with a flashlight and can't seem to see thru the shell. If eggs are not fertile how long before they will start to smell if they are bad?
Whether they are fertile or not has nothing to do with them starting to smell. They smell because bacteria get inside. If bacteria gets inside, the bacteria will multiply whether or not a chick is trying to grow in there.
I don't know how long it would take for an egg to start to smell if bacteria gets inside. I've never had an egg smell. I clean my incubator real well, don't set dirty eggs, and wash my hands before I handle the eggs.
Usually I can see veins by the 7th day, but occasionally I miss some. It takes a really strong flashlight with those brown eggs and the room needs to be really dark. I don't discard any eggs until day 14, because I do sometimes miss some at Day 7. But I do sniff them all, either when I candle or when I open the incubator to add water. And often I don't candle at all or discard any eggs until the hatch is over.