Time Traveler is an achievement/trophy in Deus Ex: Mankind Divided. It is awarded for bringing Václav Koller the Neuroplasticity Calibrator before he asks for it in mission Getting in Top Shape Again.
Jensen must travel to Otar Botkoveli's casino, and steal the calibrator from his office before doing Getting in Top Shape Again. Then he can visit Koller in The Time Machine to get his augmentations repaired. Dialogue during this visit informs Koller that Jensen already has the Calibrator he's looking for, and you will be given the achievement.