A bill expected to gain approval from Congress soon means some programmers would again need to check their code for potential problems handling a calendar adjustment. Congress is proposing a four-week extension of daylight-saving time (DST), a move that could trip up applications and gadgets programmed to adjust their internal clocks according to the summer time schedule that the U.S. has kept for nearly two decades.

The IT industry will have plenty of time to prepare for the change: The extension would take effect one year after enactment of the Energy Policy Act of 2005, which likely means a 2007 start date for the new DST schedule. The energy bill won approval last week in a joint Senate/House conference committee.

The change would shift DST's start from April to March and move its end from October to November. Those extra few weeks of DST will save 100,000 barrels of oil a day, according to legislators backing the change.

It will also confuse programs set to automatically handle DST hours. Springtime changes, observed in patchwork fashion around the world, have always been an annoyance for programmers and systems administrators: Online support groups are full of workarounds and suggestions for an assortment of DST-related glitches. For example, Cisco's technical support has pages of detailed technical information about solving DST problems afflicting its servers and routers, while Oracle's online discussion forum is filled with posts from developers seeking help handling esoteric DST challenges.

Many applications rely on the operating system to maintain an accurate clock, meaning Microsoft will play a critical role in keeping the world's computers running on time if DST hours change. The company says it's not worried. "We're aware of the upcoming change and will make sure that Windows handles the transition smoothly," says Peter Houston, Microsoft's senior director of servicing strategy.

"Smoothly" doesn't necessarily translate to "flawlessly." Microsoft's support Web site contains dozens of articles related to DST hiccups, varying from broad problems - some multiprocessor computers running Windows NT 4.0 Service Pack 4 or 5 have trouble adjusting to DST - to minor oddities. In Windows Millennium Edition, the operating systems' DST adjustment accidentally reset HTML wallpaper background images to a bitmap file.