When do derailments happen?
When your goal's countdown reaches 00:00:00! The goal shown below is derailing in just under 12 hours.
Beeminder processes derailments at your goal's deadline, the end of the "Beeminder day." The default deadline is midnight in your timezone. You can change deadlines, both your default as well as the deadlines for each goal, if you'd like to.
I just derailed, but it wasn't my deadline time!
You may derail on your goal immediately if the goal's data or road is modified such that you are no longer on the yellow brick road after the changes are made. For example, deleting all your existing datapoints will almost always instantly derail you (and possibly do so multiple times); the road does not update with the data removal, and you'll end up way off track.
This usually occurs when you're adjusting or deleting previous data entries (perhaps when trying to correct weaselled data where you should have derailed already...), when trying to clear out the goal's history to restart it (don't do that), or when an autodata integration incorrectly overwrites or imports earlier data.
If this happens to you unexpectedly, please contact support and we'll help get things back to normal!