How Do I Adjust My Computer’s Time

Posted on: March 16th, 2010

We just switched to daylight savings time and that reminded me of writing a little bit on this subject. These are pretty simple things and are meant for everyone’s use.

First of all, how can you change the date and time on the computer? I found two articles which covers the procedure on Windows XP and Vista/Window7.

XP: http://www.zolved.com/synapse/view_content/26596/How_to_change_the_PCs_Date_time_and_time_zone_on_Windows_XP

Vista/Windows7: http://www.zolved.com/synapse/view_content/26598/Can_I_change_Computers_Date_Time_and_Time_Zone_in_Windows_Vista

The only thing I’d add to this is there’s a shortcut to accessing the date/time settings. If you right click on the clock located on the bottom right corner of your screen and select Adjust Date and Time it will take you there without having to go through the control panel.

I still see on many computer that the clock is an hour off. What I find in these cases that these machines were set to the “Indiana (East)” time zone. Which doesn’t have daylight savings time. Simply correcting the time zone fixes the issue.

Now if you were to just change the time, without adjusting the time zone, your computer would set itself back to the wrong time. It’s because almost all computers are running a periodic time synchronization with a server on the internet. It works just like the atomic clock but it’s not as accurate – still within the second usually. If your computer is connected to the internet but your time is off, even though the time zone is set correctly, then it means that the syncronization is not enabled, or not configured correctly.

Daylight Saving Time Woes

DST introduces complexities. Not only for people but for machines too. The recent change on the start and end date of the DST created more issues.

If you notice that your computer is not adjusting to DST automatically, then first check the time zone settings and make sure that the DST option is checked. If the computer is still not complying then this might be the case of missing updates. The change on the start and end date of the DST was made part of a Windows update. If that update is missing then the computer will continue to adjust the time at the old dates. The solution is simply check the updates and install the missing ones.

Secure Websites and the Date

There’s an interesting connection between these two things. If the date on your computer is way off (eg by years, or months) then you’ll start getting messages about invalid certificates when you are trying to go to a secure website, for example your bank. Most people’s first thought is “someone hacked my bank’s website”. Fortunately, it’s hardly ever the case. By simple correcting the date and time on the computer fixes the issue.

In order to explain why date is important when visiting secure websites I include here the rough protocol between the secure website and your browser:

1, The browser initiates contact with the secure website
2, The website sends back a digital certificate to the browser. This certificate includes a reference to who issued it, and between what dates it’s valid.
2a, If the current date is outside of the validity range of the certificate the browser will issue a warning to the user about the certificate being not valid.
3, The browser sends the certificate to the issuing company’s server for verification.
3a, If the verification fails then the browser will issue a warning to the user about the certificate being not valid.
4, The browser will use the encryption date in the certificate to communicate with the server.

From this you can see why a wrong date can cause the warning messages.

I hope this little write-up shed some light on some of the little “mysteries of time”.