Universal constants, if they change, would result in observations of the universe we could validate. Hasn’t been validated as of yet. No data seen or test devised to discern this. Doesn’t mean it didn’t occur though.
Also, the way the equations are derived, these constants are often proportionality constants. The math doesn’t predict them as a function of time. Not to say it isn’t possible, but when you derive the constants as a function of time, the time rate of change should be detectable with fine enough equipment and decent design of experiments.
To detect constants that have changed enough so that a 6,000 year old Earth is valid, we have the equipment to do this, even if the change of constants is a negative exponential.
But science can never rule out a possibility, just that the probability of that possibility approaches zero.
A fundamentalist engineer/physicists thoughts anyway.