An Apple Support Note released this week warns upgraders that an OS X Mavericks installation can be stopped cold by an "incorrect" Date & Time setting.
Here's the symptom:
After entering in an Administrator name and password for the OS X Mavericks installer you see the following message:
"This copy of the Install OS X Mavericks application can't be verified. It may have been corrupted or tampered with during downloading."
According to the note, this message may surface if "the date and time aren't set correctly on your computer." What does this mean? Well, after quitting the installer, you have to reset the Date & Time pref.
Make sure the "Set date and time automatically" checkbox is selected and the appropriate region is chosen in the field to the right of the checkbox.
Alternatively, manually set the date and time to an accurate setting (for example, the date should be set later than Oct 1, 2013).
So, the problem appears to be the date, more than the time. There was also some additional information.
If the message reappears after checking the computer's date and time, the OS X Mavericks installer has likely been corrupted or altered during downloading. Try re-downloading the installer from the App Store again with a different network connection or location.
In addition, I suggest that customers check the automatic Time Zone setting in the Time Zone tab. Location Services is a longtime Mac feature and help keep the system time correct for applications such as Mail. Location Services (the Time Zone) and the Date & Time prefs can effect other Mac services such as Back to My Mac.
Some Mac managers may be interested in setting up a local NTP (Network Time Protocol) servers. On his computing blog, Philipp Klaus, a physics student at the University of Frankfurt/Main, Germany, recently posted a how-to article on the process. It's for OS X 10.8 Snow Leopard, but should work in recent flavors of the OS.
Meanwhile, at the JAMF Nation discussion groups, Chuck FastGM3 posted a script to place several custom NTP servers in the Date & Time pulldown list. It's a long discussion, so scroll to the end if you're interested.
Now, any Mac user can put a non-Apple time server into the Set date and time automatically field. It just looks strange since you type over the Apple server info and then hit Return. The system connects to the time server each hour, at x:54 o'clock.