I've asked around a couple of O2 users and nobody has had this problem.
I like Steve have used mine regularly as an alarm and it's never failed me.
I think with over 20M customers we would have seen thousands of complaints if this were happening.
If it were an O2 time server fault it would have to be widespread.
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Sky Unlimited Broadband - Windows 10 - Nexus 4 Android 5.1.1