Well, "lord of time" could be given as a title to Xylar, because he does control past present and future unlike any vex, because he truly isn't a vex. He is forged by the darkness rather then born as a vex. The name "timeless" comes from when he banished in time, he doesn't exist in our universe because atheon, along with many other high axis minds in our galaxy put a seal on him, forbidding him from entering our world. So I guess "lord of time" does make sense, but Xylar is well known for being the one who doesn't live in time. https://www.bungie.net/en/Forum/Post/147510697/0/0