Could we also say "How many is/are eight times three? After all this seems like something that is very precisely countable.
But we're not counting anything!
We're dealing with abstract numbers "eight" and "three".
So the result is not twenty-four somethings, but simply another abstract number, twenty-four -- which I suppose works more like a quantity.
And a Google search for "how many is eight times" (including quotes) gives three results for me (well, four, but two of them are the same result) -- "how much is eight times" gives many.