Time Gentlemen Please

At one of my previous employers, in our part of IT you were always well advised to avoid being on out of hours support over the last weekend in March and especially over the last weekend in October, the reason being that these are the clock change weekends, and more often than not one system or other would not cope with the changeover particularly well. Indeed there was one system that we were usually advised to shut down overnight on the Saturday because it really didn’t cope very well with having 1am-2am twice.

Clock change problems are not a new issue, if the system hasn’t been properly coded and tested it’s quite easy to program the system against the local time and run into quite serious issues when the clocks change. The generally accepted technique is to code everything to work from UTC, which doesn’t change, and then present times in local time.

As a result, what happened today with iPhone’s all across the UK came as rather a surprise – especially as it’s not been a problem before.

I have a couple of recurring alarms. One is set for weekdays, but then I have one timed at 8:15am for church on a Sunday.

This morning it didn’t go off. The time on the phone was correct, as was the time in the clock application, but it just didn’t ring. An hour later whilst I was in the bathroom, at 9:15am it did finally go off.

Those people used to time change problems would probably be quite surprised by that – if the alarm hadn’t taken account of the change you’d expect it to go off an hour early rather than an hour late, but from testing recurring alarms are consistently going off an hour late.

What is even more interesting is how I’ve got the alarms to ring at the right time. I tried restarting the phone and changing the timezone to somewhere else and back, and also trying to change the time, none of them appear to work. The one thing that has is something that will work for people in the UK, and that is changing the timezone to Iceland.

The significant point about Iceland is that they don’t observe daylight savings – they are permanently on UTC/GMT, so in the winter their time is the same as the UK, and in the summer an hour different. Switching to that timezone and immediately all the recurring alarms start working at the correct time.

What is perhaps most surprising about the problem is that Apple have known about it for a while, as there were similar problems in Australia and New Zealand when their clocks changed. Apple however haven’t fixed it, and unless something appears in the next week are sailing headlong into a massive problem when the US and Canada change their clocks next week. Best get ready for the uproar as thousands of people who rely on their iPhones to wake them up are all an hour late…

Update Day two after the clock change, and one iPhone worked fine, the other still went off an hour late! The difference between the two is the one that worked had alarms that were recreated in the London timezone after the clocks had changed. Whilst they still rang an hour late whilst in the London zone, they work fine in Iceland. On the other the only change we made was to switch the timezone, so the alarms were created in BST.

Further comment online indicates that the problem doesn’t occur if the alarm is set to repeat every day, only if they repeat on some days in the week.

Alarms have been recreated on the second iPhone, so we’ll see what happens on day three.

2 thoughts on “Time Gentlemen Please”

  1. Interestingly, I'm pretty sure that my alarm that went off late today was created before we went to BST, when we were in GMT the last time… Maybe the bug corrupts all oldvalarms, regardless of when they were created?

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