Pevaquark has no idea what he's talking about either! Har har. I do appreciate the shoutout and it turns out that those scientists actually do challenge everything and hold fast to what is good! It turns out that scientists don't blindly assume things are constant... they figure out how to measure them!!
Some good ones to note is the fine structure constant which is equal to e^2/hc (or the charge of an electron squared divided by the planck constant times the speed of light).
A nice paper examines the upper limit on if it's changed: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.010801. Also, a separate paper as you can see the link on the wikipedia page referenced is that this constant has changed by less than one part in 100,000,000,000,000,000 each year. That's pretty constant! That is very good evidence that the speed of light has never changed and it's not an assumption!
The gravitational constant is similar: https://arxiv.org/abs/1504.00662... it changes by less than one part in 600,000,000,000 each year. Also pretty constant.
The proton to electron mass ratio... also constant. It goes on and on with real measurements, no strange philosophy here!
The weak nuclear force that governs radioactive decay - also constant. How do we know? The smashingly good success of Big Bang Nucleosynthesis which is based upon the mass of the neutron, proton, expansion rate and radioactive decay rate which perfectly predicts which elements would have been created in the first 20 minutes of our universe. Turns out that's not changed either.
Also, if you change 'c'- you also change the energy mas relationship E=mc^2... so to get light here from billions of light years away on say day 4 of Genesis - you would accidentally increase the energy contained in matter by a factor of a million trillion - instantly creating blackholes in every planet and star in the universe, ironically killing everything that would have existed at the time.
There is no evidence of anytime of any of these ever changing as @jammycakes stated.