Maybe at IB but not necessarily at other brokers. For instance at AMP overnight margins only apply between 5pm and 6pm US ET ie when the futures exchange is closed. All other times ie.nearly 23 hours a day only $500 is reqd for YM margin. Not saying if this is good or bad - just stating what it is. PS of course overnight margins apply across the weekend as well.
i think day trading margin is supposed to work only during US session hours
i know if you hold a position from day into night, you'll get a margin call