'Appointed Time' in the Bible

And God said, "Let there be lights in the vaulted dome of heaven {to separate day from night}, and let them be as signs and for appointed times, and for days and years,

But my covenant I will establish with Isaac, whom Sarah shall bear to you at this appointed time next year."

Is anything too difficult for Yahweh? At the appointed time I will return to you {in the spring} and Sarah [shall have] a son."

And she conceived, and Sarah bore to Abraham a son in his old age at the appointed time that God had told him.