The fact that it took six days, that is, six time periods, to complete the creation of the universe implies that some period of time was also necessary to complete the creation of each of the individual entities that make up the universe.
Furthermore, the way the Genesis account reckons each day reveals something about the passage of time required for the creation of an entity. The account has an unusual way of numbering each day of creation.
When the first day of creation was completed, it states, “There was evening and there was morning, one day” (Gen. 1:5). One would think that the arrival of the morning after the passage of an evening and a night would be reckoned as the second day, yet it is referred to as the first day.
The Bible states “one day” to show that a created being must pass through a growing period, symbolized by the night, before it reaches perfection in the morning. Then, as it greets this new morning, it can step forward and realize its ideal of creation.
All phenomena occurring in the universe bear fruit only after the lapse of a certain interval of time. All things are designed to reach completion only after passing through a set growing period.
Sun Myung Moon