We're three dimensional beings who can't control the 8 dimensions above us that think time travel isn't as easy as folding a piece of paper to beings who operate in five-dimensional space
. It's not that some aliens are hypothetically time travelers, any civilization that can span millions of light years to reach our planet by necessity needed to defy the speed of light limit. Once you travel faster than light you also travel back in time, time travel would be a byproduct of exceeding light speed. And if they are defying or bypassing the speed of light limit chances are that they are operating beyond the fourth dimension(time) to begin with. Yes, aliens visiting us would probably not be operating in linear time.