That's every bit as valid a thought experiment as the ones I listed earlier.
Not really, because the very act of time travel may be what sets the future in an un-alterable state, or cause the event to happen in the first place. You are unable to separate the experiment from the result. There is no way to verify or falsify the validity of the thought experiment. And there is no conclusion that can be mathemathically or logically reached, it's just "whatever I want the answer to be". There is no "experiment" aspect to it at all.
You are quoting it as an authority on the subject, and alleging that an absence of the mention timelessness renders the argument a joke. That tactic is a joke to me, unless you are a person who believes in the Bible as the sole source of truth on these matters. I do not subscribe to that view.
It's not a tactic. The "God knows everything" crowd is attempting to use it to prove their point. It's fair game to use it to show what they claim about God is not actually what the Bible says. It's source material.