The launcher countdown can be changed by going to Settings > launcher > Countdown Timer. To change the background images, kindly go to editor mode, you will see an image icon at the upper left.
Me neither. On Wp 4.8.2 after uploading the image when you click on the insert button it stucks on a white page doing nothing. The image is in the library but not on the page. The same for the logo.
I tried on an older WP version (4.4.11) and it works. So I think you should fix the release for 4.8.2.
I am still not able to have different images display. It seems like I am able to change them, and they show up in the Preview, but when I log out and get the public coming soon page, it is the template images that are showing.