Code:
create table #ExamDur(DtTm datetime,startTm datetime,EndTm datetime,Duration int,duration1 varchar(20))
insert into #ExamDur(DtTm,startTm,EndTm,Duration,duration1)
select UE.CreatedDtTm,ED.StartTime,ED.EndTime,
datediff(mi,ed.starttime,ed.endtime) duration ,
cast(datediff(mi,ED.StartTime,ED.EndTime)as varchar(20))+':'+
cast(DATEPART(SECOND,(ed.EndTime-ed.StartTime) )as varchar(20)) Duration1 
 from UserExamMap
...