Q time was a term used by Q to describe the differences between the passage of time for the Q Continuum and the space-time continuum.
In 2378, Q suddenly appeared in Captain Kathryn Janeway's ready room and was followed shortly by his father, Q. Janeway was shocked by the younger Q's appearance as a teenage boy given that he was a toddler when she last saw him five years previously in 2373. Q explained to Janeway that because of Q time, he had aged more than normal. (VOY: "The Q and the Grey", "Q2")