declare @test table
(
NEWKEY int,
 OLDKEY int,
  [TIME] datetime
  )
  insert @test
  values(51, 42, '01/16/2013 10:00:15AM'),
  (58, 56, '01/16/2013 10:00:58AM'),
(40, 62, '01/16/2013 11:05:00AM'),
(78, 40, '01/16/2013 11:33:00AM'),
(68, 78, '01/16/2013 12:08:00PM'),
(55, 38, '01/16/2013 12:09:00PM')

;With StackDetail
AS
(
SELECT t1.NEWKEY,t1.OLDKEY,t1.[TIME],CAST(t1.NEWKEY AS varchar(11)) AS [KeyPath]
FROM @test t1
LEFT JOIN @test t2
ON t2.OLDKEY = t1.NEWKEY
WHERE t2.NEWKEY IS NULL
UNION ALL

SELECT t.NEWKEY,t.OLDKEY,t.[TIME],CAST(s.[KeyPath]   AS varchar(5)) +CAST('\' AS char(1)) + CAST(t.NEWKEY AS varchar(5))
FROM StackDetail s
JOIN @test t
ON t.NEWKEY = s.OLDKEY
)

SELECT  LEFT(KeyPath,CHARINDEX('\',KeyPath+'\')-1) AS NEWKEY,OLDKEY,[TIME]
FROM StackDetail
ORDER BY [TIME]

output
---------------------------------
NEWKEY	OLDKEY	TIME
51	42	2013-01-16 10:00:15.000
58	56	2013-01-16 10:00:58.000
68	62	2013-01-16 11:05:00.000
68	40	2013-01-16 11:33:00.000
68	78	2013-01-16 12:08:00.000
55	38	2013-01-16 12:09:00.000