I found this on the web, I don't have a Mac so can't try it. If someone does please let me know if it worked.

From the Apple Menu, open the System Preferences window.

Click the Date & Time icon in the System section of the window.

In the Date & Time window, click the Network Time tab.

Click to activate the Use a network time server checkbox, if not already checked.

In the "NTP Server" field, type "0.north-america.pool.ntp.org", then click the Set Time Now button.
After you click the button, a status message will appear:

"Synchronization Succeeded"

"Synchronization Failed. Your NTP Server may not be responding."
If you receive this message, you may wish to check your spelling in the "NTP Server" field. After adjusting your server settings, click the "Set Time Now" button again.

Optional: To freeze your settings, click the lock icon in the lower left corner, captioned as "Click the lock to prevent further changes."
Close the Date & Time window.