To get the seconds waited you can use this:
select VehicleId,
        SUM(DATEDIFF(ss,StartTime,EndTime)) Seconds,
        Count(*) Count
  from [dbo].[Table_Detail]
 group by...

I think dynamic SQL is the way to go with this, but if you were to do it with normal SQL you would end up with something like this:

Does it work if you put a DISTINCT in the SQL?
SELECT [Masjien], aliasname = STUFF(( 
SELECT DISTINCT N', ' + Aliasnaam FROM Oesskattings 

I think you are asking a question about Oracle in a SQL Server forum.

INSERT INTO MyTable2
SELECT x.AttributeName, x.AttributeValue
FROM myTable
CROSS APPLY(values ('WillField',WillField),
                    ('Surname',Surname),
     ...

@Batchsize is the number of rows it deletes each time it goes round the inner loop. You need to keep this value small enough so it doesn't take too long...

This doesn't pivot the data but is a fast (and a bit more simple than yours) way to get the subset of information back that you want.
select...