Dawid, while I can appreciate wanting this feature to be simpler, it seems that you’ve got a few options at your disposal today:
- Table Calc with the diff method presented above. Very simple formula, and if you only need it for a single viz, save it as a Look perhaps so your team can recycle it easily
- Add a second Date Measure with the rendered_value formatting presented above.
Both of these would give you a solution right now that’s fairly robust.