The quote below is a reply to an e-mail sent to Steam support.
Steam said:Hello,
A staff member has replied to your question:
Hello,
Thank you for contacting Steam Support.
The post is correct, when STCC is released the subscription will automatically be applied to your account as you have the preordered subscription.
We are unable to release the specific date for the release until it has been officially announced, but the release will be coming soon.
Please let us know if you have any other questions.