It is easy to set scheduler to work 5pm till 9am with a single 'Daily' setting, however at weekends I would like to monitor from 5pm Friday till 9am Monday - how do I do that? Obviously I want this to happen automatically every week rather than having to set it week by week using the calendar.

Security Monitor Pro has a flexible scheduling system. To monitor during weekdays, create a weekly schedule for Monday through Friday starting at 5PM and ending at 9AM. Now create a second weekly schedule for Saturday, and Sunday, starting at 9AM and ending at 8:59AM. This will cover the weekday nights and the entire weekend through Monday morning at 9AM. More details on scheduling is available here.