6th of September is a public holiday in the US (Labor Day), it's quite unlikely that anything will be released then.
Why would that matter really. Most likely the demo will be released through steam and they can set it up so it will be released on that day. There really is no need to have a person to push the button to release it. Also why would a holiday be bad they to release there would be a lot people who might be playing the game on that day as they don't have to work.