On your desktop open the  "Outlook - email/calendar application".

Click here "Outbox" (Here you can see all emails waiting to be sent).

To Enterprise Applications, (no subject), Sent None, Size 11 KB, Flag Status Unflagged, 

Uncheck the "Do not deliver before" check box. 

To Enterprise Applications, Subject Hello, Sent Mon 9/18/2023 11:29 AM, Size 12 KB, Flag Status Unflagged, 

Microsoft Outlook is an email application. In addition to email client services, Outlook includes features for managing calendars, tasks, contacts, and notes, helping users stay organized and productive. Learn how to manage your account, set up your Outlook email signature, specify out of office hours, and much more.

How to Send a Delayed Delivery Email in Outlook