In MTA build 5.5.2580.0, the MTA was changed to use coordinated universal time (UTC) rather than local time in a number of places, to avoid local time and daylight saving time issues.
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XCON: MTA Mishandles Deferred Delivery Messages After Daylight Saving Time Changes
The Timer Checking routine compared the last time that Timer control blocks (CBs) were checked by using system time. The Timer CB setup routine read the last check time by using local time. Generally this inconsistency did not cause a issue, because the MTA only looks for seconds differences, so any difference in hours was cancelled out.
However, with certain times, for example, Greenwich mean time + 5:30, the system time and local time are out by 1800 seconds. This causes all of the timer CBs to think that they have been running for 30 minutes plus the real run time and they time out in 0 seconds.