How to enter time at DST changeover?

Question

This is a clone of my stackoverflow question.

I'm working on an app that will be used by the public services (ambulance). Since those people work around the clock, they will realistically need to enter date/time values at ANY time of the day. Which also includes DST changeover times.

Now, when entering the time at the "short" day, things are easy. Simply any value between 3:00:00 and 3:59:59 is invalid. Problem is with the "long" day, where values in that same interval are ambiguous.

Is there any standard way/notation for entering time at that dreadful hour? Have you ever used any other workarounds, and which ones did your users find good?

Answer 1

Assuming the DST flip is at 3am based on your example (isn't from 12a - 1a?), you can't know which 3a someone means if they log that time. They could come in at the 2nd 3am (after the switch) or arrive at the first (before the switch).

When that time overlaps the DST changeover, you need to prompt them with something like:

1. some sort of flag to indicate -1/+1 for start/end time respectively (this could be an icon next to the start/end fields, which only appears on the day of the changeover, and even better, only if the time in the field overlaps 3-3:59)
2. an alert/popup/prompt that asks them for their total hours
3. an alert/popup/prompt that asks them before/after the change

Since it's an edge case, I don't think you need to agonize over the perfect, most usable solution, but rather just find a functional one that fits your need and possibly add a help link to explain the options.