The "Date & Time" preferences has three different parts for setting the system time and setting different options for configuring the clock.

To manually set the date and time

Click on the "Date & Time" tab.

 

Make sure to uncheck the" Set Date and Time automatically"

 

To change the date you can either click on the day in the calendar

 

or select the part of the date you wish to change and click on the up or down arrows.

 

To change the time, click the part of the time that you wish to change and click on either the up or down arrow.

You cannot manually change the time if you check "Set Date & Time automatically." This requires an internet connection and will connect to the server you choose to synchronize your computer with the correct time.

To set the time zone

Click on the "Time Zone" tab

 

Click on your approximate location on the map. In the drop down box below, select your area. You should set your time zone appropriately, as this information is used server if you set your computer to "Set Date & Time automatically".