Table:
text: 1931 Grand Prix season
European Championship Grands Prix
European Championship Grands Prix
Name_ Circuit Date_ Winning_drivers Winning_constructor Report
Italian Grand Prix Monza 24 May Giuseppe Campari Alfa Romeo Report
Italian Grand Prix Monza 24 May Tazio Nuvolari Alfa Romeo Report
French Grand Prix Montlhéry 21 June Louis Chiron Bugatti Report
French Grand Prix Montlhéry 21 June Achille Varzi Bugatti Report
Belgian Grand Prix Spa-Francorchamps 12 July William Grover-Williams Bugatti Report
Belgian Grand Prix Spa-Francorchamps 12 July Caberto Conelli Bugatti Report

Question: When was the European Championship Monza circuit in the 1931 Grand Prix season?