It can be convenient to prepare an email to send in advance of when you actually need to send it. Outlook provides you if an option to delay the delivery until a specified time.
1. Write your email.
2. On the "Options" tab and click "Delay Delivery."
3. In the "Properties" dialog box set the "Do not deliver before:" field
4. Click Close.
5. After you hit Send, the message will be held until the specified time for sending.
Information taken from: http://www.pcpro.co.uk/features/388939/the-18-best-outlook-tips-for-increasing-productivity-become-an-outlook-expert-with-these-lesser-known-tips
These instructions can also be found on SharePoint in the Software Users Group > Shared Documents > Outlook-Office 365 > Writing a Message to Be Delivered at a Future Date.