Basta juntar a tabela a ela mesma:
SELECT t1.OrderNo,DATEDIFF(day,t1.LoadedStartDate,t2.LoadedStartDate)
FROM UnnamedTableFromQuestion t1
INNER JOIN
UnnamedTableFromQuestion t2
on
t1.OrderNo = t2.OrderNo
WHERE t1.OpNo = 1 and
t2.OpNo = 4
