The date format can be changed in the new version of the watchlist for the premier date, date added, last updated, start and finish date. I think it should also be applied to the list edit section of a drama (in advanced) when actually selecting the start and finish date, or there should be a separate option to change the date format there too. In the settings, when selecting one's birthday, the date format is also locked to the MM-DD-YYYY format, although this is quite a minor issue, as this is something only filled in once, whereas the start/finish date of dramas is something I fill in manually more often than not (or at least double-check).
