If you have created some emails and used the 'Send Later' option then all of those emails will be stored in the 'Outbox' folder located in the 'Local Folders' account. Click on the 'Outbox' folder to see the list of unsent messages. You can check they are ok or delete any you do not want to send.

To send now - all messages in Outbox Right click on the 'Outbox' folder and select 'Send unsent messages' OR via 'Menu Bar' toolbar: 'File' > 'Send unsent messages'