Post immediately through the Content Library
Navigate to your Content Library, located under the Create section on the lefthand of your screen.
Find the post you want to publish immediately and click the Post Now button. (will post to whichever accounts are selected as default for that piece of content)
You can then Select All Accounts or click the corresponding checkmarks for each account you want to publish to.
Click Post to Accounts
The "Post Now" Feature
This feature is another way to quickly create new content and publish immediately to multiple accounts.
This is great if you need to post a quick update that you don't already have content made for yet.