The U.S. Energy Policy Act of 2005 changed daylight-saving-time dates beginning in 2007: the shift to summer time moved to the second Sunday in March, while the return to standard time moved to the first Sunday in November. Many operating systems, applications, appliances, and embedded devices had been built around rules that had remained stable for roughly two decades. Organizations had to install vendor patches or manually update systems handling timestamps, including e-mail, calendars, scheduling software, automated backups, authentication systems, personal computers, and video recorders.
The failure mode was operational rather than catastrophic: unpatched systems could display incorrect times for three weeks in March and one week in November, causing scheduling, synchronization, and authentication errors. The source reports isolated glitches involving Google AdWords and Microsoft Windows users, while advance preparation prevented major disruptions. The FDA nevertheless issued a preliminary public-health notification warning that some medical devices and hospital equipment might generate adverse events that were not obvious to clinicians. The episode demonstrated the costly dependence of interconnected systems on government-maintained time rules, including cross-border coordination with Canada.