Aggregate Total in a Non-GI custom page

I’m noticing a few things:

1. The ‘Footer’ is enabled through the ‘Levels’ node:

   

2. The ‘Mon’ - ‘Sun’ fields have two properties enabled: AutoCallBack, RenderEditorText (this might have to do with the PXTimeSpan)

3. In ASPX, the grid has a databinding event configured:
   <px:PXGrid ID="gridDetails" OnRowDataBound="gridDetails_OnRowDataBound">
   
   And in \Pages\EP\EP308000.aspx.cs:

   protected void gridDetails_OnRowDataBound(object sender, PXGridRowEventArgs e)
   {
       ComputeTimeTotals(sender as PXGrid);
   }
   
   private void ComputeTimeTotals(PXGrid gridDetails)
   {
       const string timeFormat = "{0:00}:{1:00}";
       (string, string)[] fieldNames
           = { (typeof(EPEquipmentSummary.mon).Name,
                   typeof(EPEquipmentTimeCard.monTotal).Name),
                 (typeof(EPEquipmentSummary.tue).Name,
                     typeof(EPEquipmentTimeCard.tueTotal).Name),
                 (typeof(EPEquipmentSummary.wed).Name,
                     typeof(EPEquipmentTimeCard.wedTotal).Name),
                 (typeof(EPEquipmentSummary.thu).Name,
                     typeof(EPEquipmentTimeCard.thuTotal).Name),
                 (typeof(EPEquipmentSummary.fri).Name,
                     typeof(EPEquipmentTimeCard.friTotal).Name),
                 (typeof(EPEquipmentSummary.sat).Name,
                     typeof(EPEquipmentTimeCard.satTotal).Name),
                 (typeof(EPEquipmentSummary.sun).Name,
                     typeof(EPEquipmentTimeCard.sunTotal).Name),
                 (typeof(EPEquipmentSummary.timeSpent).Name,
                     typeof(EPEquipmentTimeCard.weekTotal).Name) };
   
       EquipmentTimeCardMaint graph = ds.DataGraph as EquipmentTimeCardMaint;
       EPEquipmentTimeCard timeCard = graph.Document.Current;
   
       PXGridLevel gridLevel = gridDetails.Levels[0];
       HashSet<string> uniqueKeys = new HashSet<string>();
       Dictionary<string, PXGridColumn> footerColumns
           = gridLevel.Columns.Items.Where(x => uniqueKeys.Add(x.DataField))
                 .ToDictionary(x => x.DataField.ToLowerInvariant());
   
       foreach ((string fieldName, string totalFieldName) in fieldNames) {
           PXGridColumn footerColumn = footerColumns[fieldName.ToLowerInvariant()];
           int timeValue
               = graph.Document.Cache.GetValue(timeCard, totalFieldName) as int
               ? ?? 0;
           TimeSpan timeSpent = TimeSpan.FromMinutes(timeValue);
           string formattedTime = string.Format(
               timeFormat, (int)timeSpent.TotalHours, Math.Abs(timeSpent.Minutes));
           footerColumn.Footer.Text = formattedTime;
       }
   }

As a side note, in Modern UI, this is much easier, as indicated here.