AnonyMiss, We definitely do the opening of windows at night, it does get cold so that is great! :) I am mostly referring to mid-day 2-5ish because the sun is on the side of our house where we are most at (ie living room).
Having it cool at night doesn't do anything for us if it's not cool during the day..
the coolness depends on where your house is located. We are lucky enough to be in a spot where it stays cool most of the time. But when its hot the best way to keep it as cool as possible is to put fans in the windows leave them on all night and morning. Just before it starts to warm up close up your house and make it as dark as possible. We came from 29 Palms and this is no where near hot to us. Once you live there 70 is cold. Lol
This is what i would do if i was you and it summer time, go to lowes and buy an window air condition unit for around $ 200 or less and install it into the window, Now i don't think you pay for electricity where you live which is good news and you have 90 days to return it with no question ask, just hold onto the receipt and the box. I hope this help. I've done it before.
Our upstairs turns into a sauna! We have the blackout curtains, we open the windows at night and close them when it starts getting hot and all that other fun stuff. It makes it a bit cooler but it still feels warmer than the rest of the house. We just use a bunch of fans.
if maintenance see's that you've installed an AC unit they can have you remove it. At least that is what my understanding is. I think it was in our lease. Also we will be paying for excess electricity use within the near future so it could cost you as far as utilities charges. We keep our windows cracked upstairs pretty much at all times unless we are gone during the summer. Box fans placed to circulate the air also helps. Hope you all stay cool this summer!! I hear it'll be a hot one... Beach??
What I do (that works really well!) is to open all of the windows on the ground floor, and then only open one bedroom window upstairs. Make sure it's the window the farthest from the door, so that the air can circulate around the whole room. Put a box fan in the window so that it blows air outside. Because heat rises and it's usually cooler downstairs, the box fan creates like a mini vacuum effect, blowing hot air from upstairs out, while cooler air flows from downstairs to replace it. This obviously only works when it's cool outside, so hopefully this will cool down the house enough at night to have some residual coolness during the day. In the morning, even when it's still cool outside, I would shut everything to hold it in. The house will stay cooler if you lock in the colder air from night, than continue to have the less cool air from morning circulating through. Good luck!