After you take the initial steps in creating a new notification (see the FAQ "How do I set up a Notification?") and click CONTINUE, the next page of settings may include the option Schedule/State. 

The scheduling options can include Always and CREATE A NEW SCHEDULE. If you choose to make a custom schedule, you'll be able to name it and designate the days and times when notification emails are sent. Don't forget to save your schedule by clicking CREATE. 

For appropriate event types, State options are included. For instance, you might only want to know about door sensors opening or closing when the system is Disarmed. 

Make the desired settings and don't forget to SAVE.