dd command finished very quickly but does not transfer data
Everything is OK except that you shouldn't use ~ in dd commands (it's not forbidden but error-prone) and of=~/dev/disk3s3 is a file in your /Users/yourusername/dev folder (which probably wasn't intended but explains the 326 MB/s) instead of the real destination /dev/disk3s3.

So better enter:

sudo dd if=~/Desktop/Windows.iso of=/dev/disk3s3 bs=1m


or much better

sudo dd if=/Users/yourusername/Desktop/Windows.iso of=/dev/disk3s3 bs=1m