In H.G. Wells' The Time Machine, the time traveler uses an open-air time machine that does not immediately teleport through time, but rather speeds up time for the person inside the time machine. So, let's say that while time traveling, the Time Traveler, unfortunately, gets struck by something, which is very likely considering that to someone not riding the machine, the machine is going very slowly through time, making it easy to hit. Is is plausible to design a time machine such that it splices the rider off into a separate small universe bubble and re-inserts them back into the original universe, to prevent disasters like this from happening?
There is an argument to be made that this 'bubble' is a natural side effect of time travel already.
Your open air time machine is speeding through time, but not space (we'll just hand-wave the implications of this for now as it's out of scope of this question) but the rest of the surrounding environment is not. That means that there has to be some form of localised field, or boundary, inside which the time field is in effect, outside of which it isn't.
When you think about it, this has to be the case if anyone is going to survive. After all, if it was just you and the time machine, it would make it a lot harder to breathe if the oxygen molecules entering your nose end up 3 months in the past before they reach your lungs.
So let's assume a boundary exists. The next question to ask is whether or not things can permeate that boundary. I'm going to say no, because the boundary presents a lot of issues for relativity in particular. What we're describing is in essence someone travelling at the speed of light (or faster) while standing still.
In this case, one of two things are likely to happen;
1) The field boundary would appear from the outside to be a perfectly black, solid sphere, because light would not be escaping it or bouncing off it.
2) The field would cause a devastating shockwave through time that would wipe out anything in relative (no pun intended) proximity through the entire body of time through which it travels.
Either way, I wouldn't be touching it. I wouldn't be going anywhere near it, and I certainly wouldn't be throwing anything at it.
So, even if it was proven by someone that the time field boundary was permeable, this increasingly hypothetical someone would not be me. Certainly not by direct experimentation at least.