RoisinL
Finch eggs hatch 14-15 days after the hen starts sitting tight. "Sitting tight" is when the female hen sleeps and stays on the eggs non-stop, leaving only to eat drink & stretch.
I have one society hen that sits tight on day one of the first egg. My other hen doesnt sit until day 3 when the 3rd egg is laid.
If she laid 6 eggs, and didnt sight tight or start incubation until the last egg was laid, that would add 5 more days. Meaning 20 days from the 1st day the egg was laid.
In case you misjudged the date of incubation, I would let them sit on the clutch another week. And if you start to see babies hatch, dont throw away unhatched eggs (unless you are sure they aren't viable). With societies it is common for them to have eggs hatch days later than the first hatchlings. Their larger siblings are usually very gentle and considerate of the newborns.