By Monday 21 at 10am the two clubs must have a deal
Past 11.30pm on Thursday the Competition Committee published their resolution on the Clasico.... and after a lot of debate, the main consequence is that the game cannot be played on October 26 because of the political tension in Catalonia. There will be no change of stadium and instead the teams must agree on a new date.
They have until Monday 21st October to do that, at 10am, and if not then the committee will find a date. The 18th of December, a Wednesday, and the 7th, a Saturday, have been suggested.
To play midweek would be a blow for the audiovisual interests of La Liga, with the weekend being better for people to watch on TV. Furthermore there are Copa del Rey games that day for all clubs in La Liga apart from the four competing in the Spanish Super Cup - Real Madrid, Barcelona, Valencia and Atletico Madrid.
Having a Clasico on that day would be bad for the Copa, as many would stay home to watch it. December 7 could work. The games against Espanyol (v Madrid) and Mallorca (v Barcelona) already on that weekend would move a few days earlier - Dec 4. Neither opposition would complain about that change.