Hello,

I just wanted to know if you were able to solve your issue based on the Brian suggestion or you still need help? Just let me know.
Thank you.

Sincerely,
Dimi
Developer Support Engineer
Infragistics, Inc.

You could implement the ICustomSummaryCalculator interface and assign that implementation to the SummarySettings.CustomSummaryCalculator property (you must also set the SummarySettings.SummaryType property to 'Custom').

Example:
public class CustomSummaryCalculator : ICustomSummaryCalculator
{
    private int totalMinutes = 0;

    #region ICustomSummaryCalculator Members

    void ICustomSummaryCalculator.AggregateCustomSummary(SummarySettings summarySettings, UltraGridRow row)
    {
        object value = row.Cells[summarySettings.SourceColumn].Value;
        if ( value is int )
        {
            this.totalMinutes += (int)value;
        }
    }

    void ICustomSummaryCalculator.BeginCustomSummary(SummarySettings summarySettings, RowsCollection rows)
    {
        this.totalMinutes = 0;
    }

    object ICustomSummaryCalculator.EndCustomSummary(SummarySettings summarySettings, RowsCollection rows)
    {
        TimeSpan ts = TimeSpan.FromMinutes( this.totalMinutes );
        return string.Format( "{0}:{1}", (int)ts.TotalHours, ts.Minutes );
    }
}