According to carbon 14 dating how old is the iceman
So, rather than 'c' being constant with time, it has been proposed that the product 'hc' (where here 'h' is Planks Constant and 'c' is the speed of light in a vacuum) should be considered constant, see Setterfield.
Even in recent times, hundreds of measurements of 'c' since 1675 show a small but statistically significant decrease i.e. The Effect of Changes in 'c': It is well known that the radioactive decay 'constant' K can be changed i.e. In particular, Setterfield has shown that K is strongly related to 'c'.
The Institute for Creation Research (ICR), The Center for Scientific Creation, The Creation Science Movement, and Genesis Science Research.
The secular scientific community does likewise e.g.
Creationism believes that the universe and all living organisms originate from the Creator God of the Bible.
On this definition a theistic evolutionist could also be described as a creationist simply because they believe God created all things.
But the usual assumption of Creationism is also that no macro-evolution is involved, and so all living organisms were created substantially as they now exist, although it is accepted that small changes (micro-evolution) within created 'kinds' (Gen 1.25) do occur.
On this definition it is not necessary to assume an old earth and Young Earth (YE) Creationism is the belief that the universe and the Earth are just 6,000 to 10,000 years old as inferred from a literal interpretation of the Old Testament.