When you come to Options, by default you see the General options and get a window as shown below:
Figure 1: General Options Tab
Default Time Mode:
Here you can set the default time mode for the EventViewer. With this option you specify the time-frame which will be recognize by the EventViewer. For example "Last 24 hours" only displays Events which were generated within the last 24 hours. This time mode will be used for every view by default.