Having the correct date and time in Sonar can be crucial for some features of Sonar to function correctly (such as authentication). It is generally important to have it synced with the same time as your Domain Controllers.

Sonar 3.2.14 and Below
You can, however, manually set the date and time yourself via the GUI if need be. This can be done in System -> Date/Time. From here, you can select the correct Time Zone and adjust the correct time if it is incorrect. The System WILL need to be restarted for changes to take effect.

You can also change the NTP settings in System -> System Files -> NTP. Generally, you can leave the default NTP servers unchanged, but you can add other time servers if you prefer. You must use an IP address or a fully qualified domain name (FQDN) such as mytimeserver.domain.com of a time server on your LAN or on the Internet. Click "Apply" to make any changes.  

Sonar 3.5
With Sonar 3.5, because of Red Hat Enterprise, it has it's own Date/Time functionality, therefore the option in the Sonar GUI is now removed. To adjust your timezone in 3.5, it will have to be done via the command line, running this command:

ssm -t set_timezone

This will then prompt you to enter your country and state, for example:

Australia/Victoria
Australia/Queensland