If the air cools down significantly at night, you can open a window and put the fan in exhaust mode, which siphons hot air out and pulls cool night air in.

Do window fans actually help?

Window fans can effectively cool your home in seasons when it is hot during the day and cool and dry at night and also during chilly days. The fans will save you from having to run the air conditioner, which will lower your electric bill and benefit the environment.

Is it better to have a window fan blowing in or out?

From a purely temperature point of view, not human perceived level of hotness, it is better to point the fan outward. This is because the fan motor will dissipate some heat, and when the air is blown outwards, this heat goes outside.