I came across this problem whilst working on generating the total non activity time within an incident. (this post if your interested) and though i'd just post a little bit on this to complement my other post.

 Anyway essentially the problem lies when you view the Resolve Case dialog box in Microsoft Dynamics CRM 3.0, an incorrect total time is displayed for the billable time. For example, the Actual Duration field displays the default value of 30 minutes. Additionally, I noticed this when I calculated the total time spent on an incident by using the Microsoft CrmService Web service, the CalculateTotalTimeIncident message returns an incorrect total time of 30 minutes.

There are a couple of documented workarounds for this problem, the one i used was as below

• Include Actual Duration,Actual Start and Actual end in your entity form(hide if you wish)
• Enable the OnSave event and add the following code into it.

            crmForm.all.actualdurationminutes.DataValue =
            crmForm.all.scheduleddurationminutes.DataValue;
            crmForm.all.actualstart.DataValue = crmForm.all.scheduledstart.DataValue;
            crmForm.all.actualend.DataValue = crmForm.all.scheduledend.DataValue;

• Save and then publish the customisation

 hopefully this will be of some use to you