Dynamically Change Default Timestamp Provided

Hey folks, I have an action that takes in a start timestamp and an end timestamp. I would like to configure defaults so that when a user changes the start timestamp, the end timestamp automatically updates to some specified time after (though the user can choose to change this default). I can do this pretty easily in workshop but I find it difficult to specify this logic in the action form/access the form entries as variables in workshop to do this. Is there a better way I can achieve this directly in the action specification?

I’m not sure how you would accomplish this in the Action configuration, but if I were in your position I would consider rolling my own Action form using an Overlay + relevant input widgets. That way I could have variable values update in response to user input.

Is it simply for a better user experience, or are you concerned that the submitted end timestamp could be before the start timestamp?
In the latter case, you could convert your action to be function-backed and throw a user-facing error to ensure such invalid timestamps can never be submitted.
In both cases, I agree with Taylor that creating your own form in Workshop would give you the flexibility you need.