I have an application in which users can enter tabular data such as:
start | value ------------------- | ----- 12:30:00 27/10/2019 | 0 01:30:00 27/10/2019 | 1 02:30:00 27/10/2019 | 2
It turns out that 27/10/2019 02:00:00 (date given in UK format, so 10/27/2019 for Americans) is the "roll back" daylight savings instant for the UK. That is, at 2am, clocks are rolled back to 1am. That is, all times between 1am and 2am occur twice, and there is effectively a 25 hour day. As such, the second row in the table above is an ambiguous time. Does the user mean the first occurrence of this time, or the second?
What is a good way to provide UX around this (This is an html/js web application so there are quite a few options graphically)? Adding another column to the table seems extremely verbose just for this edge case. Displaying date-times in UTC is not an option either, as this would make the day-to-day usage of the application quite difficult for users.