According to legitimate scientists of various disciplines, especially physicists, time travel is theoretically possible.
However, a time machine must also be able to travel in outer space. The explanation for this is that the Earth is obviously always orbiting the Sun. So if you travelled only in time you would almost certainly end in outer space because the Earth would not be where it was when you began to travel in time. It may be that when you had travelled in time the Time Machine would need to be either piloted to catch up with Earth or to wait for Earth to approach and then do a soft landing. Of course at the beginning of your journey in time and space you could set both the time and space co-ordinates (estimating where the Earth would be when your Time Machine materialised) but that would be a big risk. You could end up inside a substantial block of concrete or in a canal or in the sea etc unable to escape. You do not know what the status of the space you started at will be in the future.