1. Select the type of message you wish to send and follow the steps to send a Merge Send or an Upload Send. 
2. After completing all the steps and composing your message, select the checkbox labeled ‘Schedule campaign’.

Once selected, this option will display the  ‘Date’, ‘Time’ and ‘Tine zone’ . 

3. Select the ‘Date’ box to reveal a calendar. Then, double-click the desired date to schedule your message.
4. When you select the ‘Time’ box, a dropdown with the hour and minutes along with AM or PM slots will appear. Choose your desired time by selecting each.
5. The click ‘Schedule Campaign’ to confirm

To view or delete a scheduled message see : 

How to delete a scheduled message

How to view scheduled messages