While the fixture is provisionally scheduled for May 26, Spanish fixtures are somewhat of a moveable feast and are regularly arranged based on a number of sporting and external factors.
In the final weeks of the season, organisers usually seek to schedule games in groups across different days and kick off slots depending on permutations involving the title, European qualification and relegation. While it's very possible that the game may have been moved to the Saturday, Madrid's request adds a further factor into the mix for fixture planning department.