If you could go back to a period of time, what would it be and where?
Causality would end up with you still only eating the meal once, unless you go with that multiple universes BS variant of time travel used to excuse bad writing.
Edit: Unless you jump into that exact experience you formerly had with the chance to do it again in an overwriting fashion, but that's more magic than machine-like.
"The fact that none of them have ever surfaced or shown any evidence of it blows a gigantic hole in many of the non multi-timeline theories."
Unless they can only travel to a time that's been pre-established as time travel capable, like the movie Primer does (they can only travel to times where the machine was left on and already existed). In that sense we'll have seen no instances of it thus far, and from that cannot tell if Determinism would be the case within a single timeline or if it's really just plane shifting you to tangent realities in place of performing actual time travel.
If we are assuming time travel is possible the multiverse theory on it is by far the most logical.
I mean the main problem and paradox with we have is that if it is possible, as time goes towards infinity so would the people traveling in time. The fact that none of them have ever surfaced or shown any evidence of it blows a gigantic hole in many of the non multi-timeline theories.
It would be interesting to know what happened but there was no "before the big bang" since time began at that moment. The Big bang is also quite incomprehensible even to some scientists, so seeing it would perhaps not be very useful. Seeing the end of the universe could be more meaningful. If it ends in "heat death" which means just an empty void with a few particles floating around, you would know that everything was pretty meaningless. A big crunch is perhaps better or if a new universe is born out of the old. One should keep in mind though, that according to Einstein's theories, time is really a continuum. We are at a slice of time that we call "now" but his theories allow for someone to be both in the past and the future. This means the future has already happened and the past isn't gone. According to string theory everything also happens at once, in one single moment. It's only our limited perception that make us see it as linear. So in this moment we are born and we die, the universe is born and it ends.