Time Travel and Conservation of Mass

OK, I am not a physics expert by any stretch, so my suppositions here may be totally wrong but here goes. In fictional time travel a person can go into the past, but that would entail removing matter from the present and putting extra matter into the past, which would create a discontinuity over time in the amount of matter in the universe.

OK, that is fiction and nobody cares about that minor detail. But in actual physcis I believe there are theoretical models of time travelling particles, etc. Again I may be completely off base here. But if there is, what happens to the conservation of mass in those cases?

Please be gentle if this is a dumb question.

I think this is called the bucket problem…

Lots of previous threads on this.

Would time travel violate the First Law of Thermodynamics?

Time travel and the law of conservation of energy

What’s the matter: time travel paradox

There are many more if you want to do a search.