Ideally, any eggs destined for incubation should be as fresh as possible but in reality, eggs will remain viable for weeks before they are incubated. In the wild, turkeys lay a big clutch of eggs and probably lay an egg every otherday, so the first eggs can be pretty old before the turkey starts to sit. I've seen American wild turkeys with really big broods and the delay in sitting doesn't seem to have done the eggs or the chicks any harm.