To schedule your email to send in the future.
Click the clock icon from the top tool bar
Select date & time for your email to send
Click the red "Schedule" button in the top right corner (This is the most commonly missed step. choosing a date/time, then closing the draft will not schedule the message).
Confirm that your email is listed in your Tracker so that you know it saved your option to schedule
You can view, edit, update the recipient list, or cancel the email any time before it sends from Tracker.