@Jiangli: I agree with @ysireesha. We need to know in advance what's included in the release so that we can be prepared and plan for any (breaking) changes to be fixed early since there are only one week between the start of release deployment to sandbox and start of release deployment to production. Worst case it would be only 2 days (last day of deployment in sandbox and first deployment in production - not clear if this situation will occur).
So to sum up: we need to have the release notes earlier than the start of deployment in sandbox. If the release content changes, just make an update. Customers must have a way to rollback their changes (i.e. CVS) if something would be excluded.