Colonna calcolata DATEDIFF di SQL Server tra le righe

Ti consiglio di utilizzare una vista per questo scopo:

CREATE VIEW Table1_vw 
AS
WITH cte AS (
    SELECT  *, 
            ROW_NUMBER() OVER (ORDER BY RecordTime) AS rn
    FROM    dbo.Table1
)
SELECT  mc.RecordTime,
        mc.Running,
        mc.Fault,
        DATEDIFF(second, mc.RecordTime, mp.RecordTime) Diff
FROM cte mc
LEFT JOIN cte mp
ON mc.rn = mp.rn - 1

Poiché stai utilizzando SQL Server 2012 puoi utilizzare LEAD funzione:

CREATE VIEW Table1_vw 
AS
SELECT  RecordTime,
        Running,
        Fault,
        DATEDIFF(second,RecordTime,LEAD(RecordTime,1,NULL) OVER (ORDER BY RecordTime ASC) ) as Diff
FROM Table1
GO