Creationists reject what might be called the Deep Time Postulate (DTP): that long stretches of time existed before the earliest humans ever lived. The DTP enables uniformitarianism in geology, evolution of all species in biology, and evolution of the solar system in astronomy. DTP enables science to insert a kind of history before history, that is, before written records or human artifacts.
Without the DTP, less than ten thousand years have transpired in the universe, that is, the time since humans and other living kinds appeared on the earth as determined from human artifacts and records. Instead of the DTP, creationists accept what might be called the Demi-Creator Postulate (DCP): that a demi-creator exists (or existed) who formed the earth and celestial bodies as well as the kinds of organisms that originally populated the earth. The DCP enables large-scale catastrophism in geology and creation in biology and astronomy.
Why “demi-creator” instead of Creator? The answer is that science does not use scriptures and so a scientific creator lacks the full range of characteristics that a theological Creator would have. For the purpose of science all that is necessary is a being like Plato’s demiurge*, who is like us but with much greater power and intelligence. I am calling this being a “demi-creator” since it is a partial creator. Whether it is the same being as the Creator of the theologians is for them to decide. For science a creator-type being is like us, not creating from nothing but forming a product from something else.
From the existence of a demi-creator one may infer that the creation is intelligible by us and that it exhibits features that are recognizable by us as intelligently designed. From knowledge of some parts of the creation, we may be able to infer the character of other parts, since they would exhibit similar characteristics, as a design engineer implements an overall design in every part.
One consequence of the DCP is that the creation is finite because a demi-creator is only capable of what we could do given greater intelligence and power. Creationists take this as supporting the creation of a finite number of different kinds of organisms. Different kinds of organisms likely exhibit similar design features, in what those who accept the DTP would call convergent evolution.
* The demi in demiurge is not from demi, meaning half or partial, but from demos, common people; nevertheless, it suggests something less than divine.