Huh, no.
Any Variation in the speed of light over the history universe could be constrained to a fairly high tightness with just a nearly instantaneous observation, unless you are to make a host of additional totally unwarranted, ad hoc, unsupported claims just to protect the unwarranted, ad hoc, unsupported claim in a futile effort to the already Unsalvageable reputation of your coreligionists.
So try again.
Any Variation in the speed of light over the history universe could be constrained to a fairly high tightness with just a nearly instantaneous observation, unless you are to make a host of additional totally unwarranted, ad hoc, unsupported claims just to protect the unwarranted, ad hoc, unsupported claim in a futile effort to the already Unsalvageable reputation of your coreligionists.
So try again.