Since when was there a minimum amount of time for a theoretical computer to do any number of computations? I suppose that any computer must take some finite, n

Since when was there a minimum amount of time for a theoretical computer to do any number of computations? I suppose that any computer must take some finite, non-zero amount of time to perform an "instruction", because if the amount of time per instruction is zero, that would violate Turing's proof of the undecidability of the halting problem over Turing machines. His idea does have some merit, but I still don't think that this means there cannot be a Universal Computer -- just that it may be something that operates on a level above a Turing machine. I'd imagine it would involve some sort of recursive structure.