Daylight-saving change may confuse PCs, VCRs

For three weeks this March and April, Microsoft Corp. warns that users of its calendar programs “should view any appointments … as suspect until they communicate with all meeting invitees.”

Wow, that’s sort of jarring – is something treacherous afoot?

Actually, it’s a potential problem in any software that was programmed before a 2005 law decreed that daylight-saving time would start three weeks earlier and end one week later, beginning this year. Congress decided that more early evening daylight would translate into energy savings.

Software created earlier is set to automatically advance its timekeeping by one hour on the first Sunday in April, not the second Sunday in March (that’s March 11 this year).

The result is a glitch reminiscent of the Y2K bug, when cataclysmic crashes were feared if computers interpreted the year 2000 as 1900 and couldn’t reconcile time appearing to move backward. This bug is much less threatening, but it could cause head-scratching episodes when some computers are an hour off.

The problem will also affect plenty of non-networked devices that store the time and automatically adjust for daylight saving, like some digital watches and clocks. But in those instances the result will be a nuisance (adjust the time manually or wait three weeks) rather than something that might throw a wrench in the works.

Further confounding matters, there are lots of old computer programs whose original vendors don’t support them anymore, meaning no repair is available. Some gadgets, such as VCR clocks, may not have any mechanism to update their software.

Also, the change originated in the United States and is being followed in Canada, but not most other nations. That could befuddle conferencing systems and other applications that run in multiple countries at once.

A common fix is a “patch” that reprograms systems with the new start and end dates for daylight-saving time. Some of these updates are targeted at specific systems, while others have wider implications – such as one from Sun Microsystems Inc. for older versions of the Java Runtime Environment, which often fuels applications.

Microsoft planned to send its daylight-saving patch to Windows PCs with the “automatic update” feature Tuesday. Users with automatic updates turned off should download the patch from Microsoft.

New machines running Windows Vista are immune, since Vista was finalized after the 2005 law passed.

However, computers running anything older than the most recent version of Windows XP, known as Service Pack 2, no longer get this level of tech support. Owners of those PCs should go into the control panel and unclick the setting that tells the machine to automatically change the clock for daylight-saving time. They have to make the change themselves when the moment arrives.

For people who store their appointments in Microsoft Outlook or other desktop-based calendar programs – rather than dynamic, Web-based programs such as Google Calendar – the situation gets trickier. Patches for calendar programs are available, but appointments entered before a patch was applied might still be registered in standard time rather than daylight time – off by an hour.

Microsoft advises heavy calendar users to go online and download a small program known as “tzmove” – Time Zone Move – that can retrofit all previously booked appointments to the new daylight-saving rules.