Hello,

I was able to achieve this through the following code sample, please try it:

            for (int i = 0; i < this.ultraCalendarInfo1.Tasks.Count; i++)
            {
                foreach (Task childTask in this.ultraCalendarInfo1.Tasks[i].Tasks)
                {
                    if (!childTask.IsSummary)
                    {
                       childTask.SetDuration(childTask.Duration, Infragistics.Win.TimeSpanFormat.Hours);
                    }
                }
            }

Please feel free to let me know if a question about our tool set comes up on your mind.

Worked for me as well.  Thank you.