Saturday or Sunday morning, at the butt crack of dawn. I will finish at night (or once the sun gets to the other side of my house and my driveway is back in the shade) if I don't get everything done before the sun takes over my driveway.
Saturday morning or maybe friday morning/early evening. I typically do a rinseless wash, so time of day is not really important. I just like to try and get it done in the morning.
Usually a day that ends with "y", LOL! I see some wait for the weekend and that's always something to look forward to for sure. I see others wait for 4 days w/o rain, well, I don't trust them to be that good and my motto is this, if its clean for one whole day, well, it worth a wash to me.
I ONR in the garage. In the summer I pretty much wash it whenever it's dirty, sometimes two or three times a week. I have a small 350z, and it takes less than 30 minutes for wheels, tires (UTTGP), and car. If I really move I can do it in 20 min.