Sure! It is a rare problem, but I seem to recall a similar thing (at Facebook?) actually making the news not that long ago. Here are the steps: 1. The user in

Sure! It is a rare problem, but I seem to recall a similar thing (at Facebook?) actually making the news not that long ago. Here are the steps: 1. The user in California saves a meeting at 7am for June 1, 2017. (Today is April 17.) 2. You convert to UTC (-0700) and save that in your database. 3. On May 1st California decides to stop observing Daylight Savings Time effective immediately. Your server automatically updates its system-wide timezone file so it knows about this change. Now that UTC date in your database is happening at 6am instead (-0800). The instant hasn't changed (The meeting is still happening at the same moment in e.g. Paris.) but the user probably really wants it to stay at 7am. They are going to be annoyed if their colleagues dial in while they are still in the shower. :-) I hope that helps!