At night temperature outside is usually lower than temperature set on AC. So looks like conditioned air should not leak outside (if it does, it is replaced with even colder air) and it is fine to leave window opened. Is this correct?
Note: when window is opened but AC is off, temperature quickly rises because of hot walls and inside sources of heat.
Best Answer
If you're confidant that the air leaving the house through the open window is warmer than the outside air that will come back in to replace it, I suppose it's OK to leave the window open. But I think a better solution would be to shut the AC off and use a window fan to circulate the cool outside air through the house. A window fan will be quieter and more energy efficient than an AC, and probably faster at cooling as well.
Which direction the fan faces doesn't matter a ton as long as you're moving the air around, but if you think about the goal of getting the hot air out of the house and the cool air in, here are some ways to think about it: