Well, it is not POSSIBLE to get to Vienna in one day. Have to stopover in Munich or Frankfurt, and quite frankly Munich is so expensive and pointless WHY waste a night there? At least Frankfurt there is possibility of sex. But this means London to Frankfurt Monday (3 hours from Brussels), Tuesday morning Frankfurt to Vienna (8 hours) arrive 2pm Vienna Tuesday, spend Tuesday and Wednesday night ONLY in Vienna, Thursday morning back to Frankfurt and night in Frankfurt. Friday back to Brussels Friday night, home Saturday morning.