Are these tree swallow eggs unviable? (1 Viewer)

It's been 21 days since the last of 5 eggs was laid in my nest box, all eggs are still there, none have hatched yet If I am being realistic, is it likely they are all unviable? How long do I wait before I give up hope?

Are they still being incubated? According to BNA-online the incubation period is most commonly 13-14 days within a range of 10-20 days. That said, if it were me, I wouldn't give up hope quite yet.

They have been incubated for quite some time already.. I decided to gently take them out and candle them tonight. Holding each one up my cell phone flashlight, one egg held a dark red embryo, not moving (dried up blood explains the colour), the other 4 were clear with nothing inside I've been watching these birds from the beginning, build their nest, lay their eggs and take turns watching over their family.. I'm super heartbroken that I won't get to see any hatchlings. I think the cold spells and rain made it impossible for them to survive. Maybe next year will bring better luck