Visit your Settings page by clicking "Settings" in the top right, or use this link: https://www.workingon.co/you
Scroll down until you see "Emails." Underneath "Emails," you will find "Send me progress emails at... " To the right, you'll see a time - generally 6 AM. Click on the 6 to select the desired numeric value from a drop down, then click on AM to select AM or PM.
All Settings selections will auto-save, so there's no need to find a "Save" button.