Is time a river, or a lake?
If time is a river, then one could travel back in time, and their presence would have just as much effect as a stick, or rock in a stream. Time would flow as normal around the rock or stick, and once removed, time would once again resume it’s normal coarse.
If time is a like a calm lake, then even the smallest rock thrown into it would send ripples to the farthest shore, but let’s be honest. Not many lakes are that calm during a storm, so even throwing a rock into lake isn’t going to effect it much.
In the end I’m not sure if someone going back in time is going to effect the future that much, unles you do something like throwing a bolder in the middle of a lake.
Eventually the ripples stop, and time is just there like a pool of water.
It seems hardly fair to compare time to water, but you get the gist of it. I mean after all time happens, not much you can do about it.