title: Dynamics CRM 2011 Online - How to total the duration for activities
body: <p>I have a requirement to total the durations of all activities related to a custom entity. I have created a custom entity that allows the user to add activities for that instance of the custom entity. Every time an activity is added to the custom entity I need to total the duration and update the custom entity. I started by creating a plugin for an activity. The problem is the only messages you can create the plugin for is retrieve and retrivemultiple. I then went to service activity to create the plugin and I cold create it using the create message. </p>
  
  <p>My question is, is every activity a service activity? Has anyone done this and do you have any tips on the best way to go about it?</p>
  
  <p>Thanks,
  Gary</p>