Disclaimer: I'm not part of the QA team, but I don't know for sure if there is
other way to do this.
plasma-widget-adjustableclock has been RC buggy for more than a year. It does
only FTBFS but even if it did it requires Plasma 4 which is not available
Moreover it will not have a Plasma 5 version:
So ideally this package should be removed from the archive.
Kinds regards, Lisandro.