The Model Time Machine was a miniature time machine created by The Time Traveler shortly before his actual one. The machine was fitted with Plattnerite and worked just as well as the real machine, but was too small to carry a real occupant. He used it to demonstrate how his machine works to his friends, by sending it into the future. ("The Time Machine")
Shortly before that demonstration, he showed the model to Edward Turnbull, and intended to demonstrate to him, but became distracted when he thought of a new idea, and quickly retreated to his laboratory. Later, he left for London. ("The Space Machine")
In 1905, roughly six years later, the machine returned. H.G. Wells, the Time Traveler's friend who had written down his story, later theorized that the machine had gone all the way to the end of time which had curved around to the beginning of time, leading the machine to end up close to its point of origin. ("The Time Machine: A Sequel")