Could these eggs hatch on day 28?

[albrightcm]

I have two eggs remaining in my incubator that passed the float test but are dark shelled so I am unable to see any internal pipping. The egg is clearly full of a full size chick and the air sac looks as you would expect at full-term. Our first hatch was two chicks on day 23 late in the day with our second hatching on day 24. What is the latest these two could hatch? Do I intervene?

 

[sourland]

The late hatching indicates that your thermometer may have been reading incorrectly. It is possible, but not probable that the remaining eggs are still viable.

 

[albrightcm]

How long should I wait? I don't want to toss an egg that has a slight chance of hatching.

 

[sourland]

Have you done the float test? Viable eggs floated in warm water should show some movement. Type 'float test' in the search bar at the top of the page - information should appear.