By Philip Elmer-DeWitt
January 1, 2011

For the second time in two months, Apple’s alarm clock fails to smell the coffee

Judging by the obscenity-laden chatter on Twitter last night, a lot of iPhone owners are still depending on the device’s Clock app to wake them on time.

This is the same app that failed to adjust properly for the end of daylight saving time in November and awoke users around the world an hour early or, in some countries, an hour late.

Apple (AAPL) was reportedly aware of iOS’s so-called NTP bug before that mishap and was supposed to fix it in the new version (iOS 4.2.1) that was released Nov. 22.

The fix didn’t stick. As of the stroke of midnight last night, one-off alarms no longer go off as programmed.

Some Apple defenders are suggesting that the problem lies in the NTP algorithm around which the app is constructed. That seems unlikely. Network Time Protocol, originally designed in 1985, is one of the oldest Internet protocols still in use. Other devices not half as smart as the iPhone seem to know how to work with it.

Meanwhile, there are work-arounds. According to Engadget, the easiest is to set your wake-up time as a recurring alarm and cancel it after the clock goes off.

Or you can just wait a few days. According to our friends at 9-to-5 Mac, who seem to have spent last night troubleshooting the alarm, the problem will fix itself on Jan. 3.

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[Follow Philip Elmer-DeWitt on Twitter @philiped]

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