Thanks Ernesto, i tried both but still the output is zero, i think your sample is not applicable for data that is coming from a Sharepoint List.
I tried this but still no luck
sum(xdXDocument:GetDOM("Work Order System")/dfs:myFields/dfs:dataFields/dfs:Work_Order_System[number(translate(translate(translate(@Labor_Min_Date,'-',''),' ',''),':','')) > number(translate(translate(translate(/my:myFields/my:SummaryReport/my:LR_StartDt,'-',''),' ',''),':',''))]/@Labor_Hours_Total)