Methods for operating portable electronic devices to maintain accurate timing information are provided. In one suitable arrangement, an electronic device may have a real-time clock and a mach-time clock that can be used separately to track the Coordinated Universal Time (UTC). The offset of the real-time clock and the mach-time clock from UTC can be monitored to determine if there is any oscillator frequency drift, which can be characterized using a linear model. Any variation in drift caused by environment factors such as temperature may also be characterized. In another suitable arrangement, a primary electronic device that is capable of maintaining accurate timing information may transfer that information to a secondary user device. Timing information may be transferred using mach-time values and may then be converted to real-time clock values to ensure that the secondary user device can estimate time accurately even when the device goes to sleep.