Be particularly certain that it is set to the right month, the right day and the right time. Ensure that the AM or PM is set correctly as well as the year. Often the time will be correct but the year will not be. Likewise, it's common for the time to be correct but the AM/PM setting is out.
To make this easier here's a quick checklist for you :)
[ ] Is the Time correct?
[ ] Is the Date correct?
[ ] Is the AM/PM setting correct?
[ ] Is the Year correct?