I think that’s backwards. Not setting the timer ahead would have caused it to go off later, not earlier. The timer would have had to automatically set itself to daylight time while he had the trigger set on standard time to produce an earlier explosion.
Unless the bomb clock was connected to an automatic update service like cell phones are, it would remain internally consistent and not be affected by the DST change. This article doesn’t make sense.
Maybe it was a Y1K problem.