Local Planetary Time was a forerunner of stardates. The system came about when colonists on Mars needed to reconcile Martian sols with Earth hours. A council of religious scholars on Mars came up with Local Planetary Time, which was based on Vulcan look-up tables and charts that Vulcan ships had been using to keep their time that of Vulcan. When Humanity began to colonize more planets and send starships on longer missions, Local Planetary Time was supplanted by stardates. (DS9 - Millennium novel: The War of the Prophets)