Started to find eggs how long are they alright to eat

I found a small egg in our dog igloo we have on the porch (for the neighbor's barn cats) the other day I think Tuesday?! .

Husband was afraid of it

I know it wasn't there any longer then 48 hours I think I might have checked there so I think it was even in the 24hr range??
BUT we marked it and put it in the nest box.

I think I have 3 hens laying or about to lay (all doing the egg squat)
I got 1 small egg Wednesday nest box & got a really BIG egg in the nest box yesterday Thursday) and a thought oh good they are using their boxes..

NOW I found a nest today with 3 eggs in it Today in my cellar window box. NEVER thought to look there before
It is raining now and it is out of the rain and out of the sun (I think)
One was just laid. It was still very warm and still wet. and she was hanging out there squalling. I came back when she was just leaving to see 3 eggs.

She hasn't laid (well I haven't found them) any for about week to 2 weeks?. But I have been finding lots of shell less eggs laying around the yard under the porch & in their coop.

How can I tell how long the eggs have been there?

I heard about the float test about if they sink. So I got the one we put in the nest box (5 days ago) that we marker (thinking it would at least float some but they all sank straight to the bottom. no hesitation they don't even bob. Does this mean that they are all ok to eat? Or is this to tell if they are not fertile?

I have no roosters but a duck who I have seen try to mount them.


please advise how long is to long to find a nest in the shade?