In his book Three Roads to Quantum Gravity, Lee Smolin says that “Space is nothing apart from the things that exist; it is only an aspect of the relationships that hold between things.” I like to think of Time in the same way.
I think of time as a system of location, similar to how we can use the term “space” as a system of location without necessarily talking about that big starry place up in the sky.
Just as an object has a position in space it has a position in time. That position in time may place it further away from your position in time, but only in the same sense that a tree in Brooklyn has a set position in relationship to your position in Los Angeles.
Being a system of location, I believe that time can be traveled just like space can be traveled (although perhaps not by actual humans). In physics, there are plenty of studies around things such as tachyons, Bose-Einstein Condensates, loop quantum gravity, and black (and white) holes which suggest that some forms of matter (or at least information) may be capable of traversing this system of time.
One of my main issues with this concept though, is that these systems always measure time against the ruler of light (i.e. how fast a photon was able to move from point A to point B). If something has moved faster than a photon (traveling at the speed of light) it is said to have traveled back in time.
I’m not sure I like time being defined as simply the movement of light. Even if you were in a sealed vacuum of complete darkness (besides the fact that you would die due to lack of oxygen) your body would still be generating light, although not on the visible spectrum. With light we come back to the comparison against photons. Once the body is dead the light is no longer generated and we can no longer be constrained against this system of time. So perhaps through death, we truly become timeless.