The time machine, it seems, will only be able to go forward, using the speed of light to beat us there. But would the return require going BACK in Time? Because of the linear nature of time, where we always move forward, we can only know the present and past. I don't really know why light would solve the issue, however. In my very ltd. understanding of Relativity and space/time, one could go back in time by applying enough force to cause it to reverse direction- though the entire universe would have to get dragged along as time "deflates". So it may be possible to travel back in time; the real impossibility is mustering the amount of force needed to pull it off.
As for the future, well, there's already light all over the universe, and it has been there since the first stars ignited, (6,000 yrs ago?). None of it is from the future, however, as we can only see light from events in the past. Again, light is part of our relative universe, and I would doubt that one could coax the photons to "get to" the future and wait there, simply because the future doesn't exist yet- there's nowhere to "get" to.