select timespan between each history status

selectspan.sql

WITH a AS
(
    SELECT
        rt.GiftID,
        rt.ActedDate,
		rt.Status,
		rt.Description,
        ROW_NUMBER() OVER(ORDER BY rt.GiftID, rt.ActedDate) AS RN
        FROM Histories rt
)
    SELECT
        a1.GiftID,
		a2.ActedDate startdate,
        a1.ActedDate enddate,
		a2.Status startstatus,
		a1.Status endstatus,
        DATEDIFF(HOUR, a2.ActedDate, a1.ActedDate) AS Duration
		FROM a a1
        LEFT OUTER JOIN a a2 ON a2.RN = a1.RN - 1
        WHERE
            (a1.GiftID = a2.GiftID) AND (a1.Status != a2.Status)
		order by a1.GiftID, startdate