> I cannot think of any algorithms with arbitrary sized inputs that have truly constant execution time.
With respect, I think you may misunderstand the meaning of "constant time" in the sense of complexity theory, i.e. O(1). Accessing an element in an array of size n is a constant time operation. See: https://stackoverflow.com/questions/7297916/why-does-accessi...
EDIT: Corrected "search" to "access"