An Example On How God’s Timing Is Perfect From Genesis 18:10/21:2 – The Bible Doesn’t Say When You P

Genesis 18:10 (KJV) 

And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him. 

Genesis 21:2 (KJV)

For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.