When KStars starts up, the time is set to your computer's system clock, and the KStars clock is running to keep up with the real time. If you want to stop the clock, select from the menu, or simply click on the Stop Clock icon in the toolbar. You can make the clock run slower or faster than normal, or even make it run backward, using the time-step spinbox in the toolbar. This spinbox has two sets of up/down buttons. The first one will step through all 83 available time steps, one by one. The second one will skip to the next higher (or lower) unit of time, which allows you to make large timestep changes more quickly.
You can set the time and date by selecting from the menu, or by pressing the time icon in the toolbar. The Set Time window uses a standard KDE Date Picker widget, coupled with a spinbox for setting the hours and minutes. If you want to re-synchronize the simulation clock back to the current CPU time, just select from the menu.
KStars can accept very remote dates beyond the usual limits imposed by QDate. Currently, you can set the date between the years -100000 and +100000. We may extend this range even further in future releases. However, please be aware that the accuracy of the simulation becomes more and more degraded as more remote dates are examined. This is especially true for the positions of solar system bodies.