Unless the weather is really hot, an egg can be left in a nest for a day or three and still be fine. In fact, in some countries, eggs aren't even refrigerated. Eggs will keep just fine at normal room temp for about a month.
If you have doubts about how long ago an egg was laid, you can keep it separate, and crack it into a cup or bowl to see if it's ok. If it isn't, you'll know because it will look nothing like a good, fresh egg. And you didn't spoil the pancake batter, because you cracked it into a bowl. I do that anyway, so I can pick out shell chips that fall in. I hardly ever get a bad one, though.
I wash my eggs, and haven't ever had a fresh one float. That's probably a pretty rare occurrence, unless you have a hen who for some reason produces eggs with larger-than-normal air cells. I've had a few tip up a bit on one end, and on closer examination, I find they're cracked. I've had ONE egg sink that was bad. (In over 15 years) It was one my dog brought up from who knows where, and left in the driveway. I took it in and washed it. It sank, just like a normal egg. But it kept rolling to one side, like one side was heavier than the other. So I cracked it into a cup to see what was up. It had apparently been out in the hot sun for awhile, the yolk was partially cooked on one side and stuck to the shell. The egg wasn't actually spoiled or rotten, it didn't stink at all. But I tossed it, just the same.
Any eggs I'm not sure of, like when I find a hidden nest somewhere, I keep separate from the ones I sell. The only ones I sell are those I gather daily from the nest boxes. When I wash them, if there are any floaters, I toss them. The ones that tip up, I hard boil. They've always turned out fine. The ones hat appear normal and fresh, I still keep only for home use, and so far, they've all turned out to be fine, except that one the dog brought up.
Just my own experience. You can candle eggs, too, and usually a bad egg will not look like a good one. It takes some practice, though, and if you have brown eggs, like I do, it can be hard to tell much.