I just added 2 albums, both with scanned covers. I did not get a timeout error when I uploaded my collection to racksandtags. Almost immediately after starting the upload I got the message that it had been uploaded successfully.
The new covers were not visible in racksandtags right away, but when I checked some hours later they were there.
It seems alright by me, although a better test will be with more data to upload than just 2 new albums.