I was going to put in a vote for missing an hour/having one twice rather than slowing down/speeding up time, as in computer logs it is much more obvious that Something Odd Has Happened when there is an hour with no events rather than two hours with half the usual number of events.

But what happens with logging in the hour that happens twice? If you have events at 01:05, 01:20, 01:59, then 01:04, 01:30, do they get sorted by time as if the 01:04 event happened first? Or does the timestamp include information about DST? Or is the order taken as the order in which log entries were appended, regardless of time stamp?

Ideally timestamps in logs are in GMT.