No exact date given but this is a quick move by Spain as they are the last big user of Medium wave in western Europe. At night, many channels especially below about 900 KHZ have some sort of Spanish station on them although only a few are of listenable strength with several having multiple transmitters on the same channel making it worse. Those in the top half of the band are less readily received. This will make multiple frequencies that are silent in the daytime also completely silent at night. The speed of AM radio's demise is surprising even for us life long fans.