With MyCTE (TheTime)
AS
(
 SELECT convert(datetime2,'1900-01-01 0:12:14.1241234') UNION ALL
 SELECT '1900-01-01 0:08:16.361' UNION ALL
 SELECT '1900-01-01 0:08:57.705' 
 )

 SELECT *
 From myCTE	

SourceTable {
  ID identity int,
  StartTime datetime2(7),
  EndTime datetime2(7),
  SomeField1 int,
  SomeField2 varchar(128),
  SomeField3 double
}

DestinationTable {
  ID identity int,
  TimeSpan time(7),
  SomeField1 int,
  SomeField2 varchar(128),
  SomeField3 double
}

SourceTable (data):
ID  StartTime                    EndTime                      SomeField1  SomeField2  SomeField3
 1  2012-04-26 13:53:43.0000000  2012-04-26 13:54:44.5448951        1234  dummytext1  9853.12354
 2  2012-10-01 12:00:00.0130952  2012-10-01 17:00:04.9845083       24778  dummytext2       325.0

The above table data needs to be processed so that it becomes the below expected destination data:

DestinationTable (data):
ID  TimeSpan          SomeField1  SomeField2  SomeField3
 1  00:01:01.5448951        1234  dummytext1  9853.12354
 2  05:00:04.9714131       24778  dummytext2       325.0

With MyCTE (TheTime)
AS
(
 SELECT convert(datetime2,'1900-01-01 0:08:00.0000001') UNION ALL
 SELECT '1900-01-01 0:09:18.361' UNION ALL
 SELECT '1900-01-01 0:13:50.705' 
 )

SELECT 
	*,
	CAST(f.q AS TIME(7))
From myCTE a1
CROSS JOIN myCTE a2
CROSS APPLY (SELECT s_difference = DATEDIFF(second,a1.TheTime, a2.TheTime)) a
CROSS APPLY (SELECT aTime = DATEADD(second,s_difference,a1.TheTime)) b
CROSS APPLY (SELECT nsFraction = DATEDIFF(ns,aTime,a2.TheTime)) c
CROSS APPLY (SELECT tt = DATEADD(second,s_difference,0)) d
CROSS APPLY (SELECT t = CONVERT(VARCHAR(8),tt,108)) e

CROSS APPLY (SELECT q = e.t + '.' + CAST(nsFraction AS VARCHAR)) f

WHERE a1.TheTime < a2.TheTime	

With MyCTE (TheTime)
AS
(
 SELECT convert(datetime2,'1900-01-01 00:08:33.580') UNION ALL
 SELECT '1900-01-01 00:08:32.579' UNION ALL
 SELECT '1900-01-01 00:08:32.581' UNION ALL
 SELECT '1900-01-01 00:09:18.361' UNION ALL
 SELECT '1900-01-01 00:13:50.705' 
 )

SELECT 
	*,
	CAST(f.q AS TIME(7))
From myCTE a1
CROSS JOIN myCTE a2
CROSS APPLY (SELECT s_difference = DATEDIFF(second,a1.TheTime, a2.TheTime)) a
CROSS APPLY (SELECT aTime = DATEADD(second,s_difference,a1.TheTime)) b
CROSS APPLY (SELECT nsFraction = DATEDIFF(ns,aTime,a2.TheTime)) c
CROSS APPLY (SELECT tt = DATEADD(second,s_difference,0)) d
CROSS APPLY (SELECT t = CONVERT(VARCHAR(8),tt,108)) e
CROSS APPLY (SELECT q = case when nsfraction < 0 then e.t + '.' + CAST(1000000000 + nsFraction AS VARCHAR)
							 when nsfraction < 10 then e.t + '.00000000' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 100 then e.t + '.0000000' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 1000 then e.t + '.000000' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 10000 then e.t + '.00000' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 100000 then e.t + '.0000' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 1000000 then e.t + '.000' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 10000000 then e.t + '.00' + CAST(nsFraction AS VARCHAR)
							 when nsfraction < 100000000 then e.t + '.0' + CAST(nsFraction AS VARCHAR)
							 else e.t + '.' + CAST(nsFraction AS VARCHAR)
						end) f

WHERE a1.TheTime < a2.TheTime	

With MyCTE (aTime, bTime)
AS
(
 SELECT convert(datetime2,'1900-01-01 00:08:00.0000001'), convert(datetime2,'1900-01-01 00:09:18.361') 
 UNION ALL SELECT '1900-01-01 00:08:00.0000001', '1900-01-01 00:13:50.705'
 UNION ALL SELECT '1900-01-01 00:09:18.361', '1900-01-01 03:13:50.7050001'
 UNION ALL SELECT '1900-01-01 23:09:18.361', '1900-01-02 02:13:50.7050001'
	  UNION ALL SELECT '1900-01-01 00:00:00.000000111', '1900-01-01 00:00:00.000000222'

)
SELECT 
	*,
	CAST(f.q AS TIME(7))
From myCTE a1
CROSS APPLY (SELECT s_difference = DATEDIFF(second,aTime, bTime)) a
CROSS APPLY (SELECT axTime = DATEADD(second,s_difference,aTime)) b
CROSS APPLY (SELECT nsFraction = DATEDIFF(ns,axTime,bTime)) c
CROSS APPLY (SELECT tt = DATEADD(second,s_difference,0)) d
CROSS APPLY (SELECT t = CONVERT(VARCHAR(8),tt,108)) e
CROSS APPLY (SELECT q = e.t + '.' 
	+ RIGHT('000000000'+CAST(DATEDIFF(ns,DATEADD(second,s_difference,aTime),bTime) AS VARCHAR),9)
) f

With MyCTE (aTime, bTime)
AS
(
 SELECT convert(datetime2,'1900-01-01 00:08:00.0000001'), convert(datetime2,'1900-01-01 00:09:18.361') 
 UNION ALL SELECT '1900-01-01 00:08:00.0000001', '1900-01-01 00:13:50.705'
 UNION ALL SELECT '1900-01-01 00:09:18.361', '1900-01-01 03:13:50.7050001'
 UNION ALL SELECT '1900-01-01 23:09:18.361', '1900-01-02 02:13:50.7050001'
 UNION ALL SELECT '1900-01-01 00:00:00.000000111', '1900-01-01 00:00:00.000000222'
)
SELECT 
	aTime, 
	bTime,
	Result = CAST(f.q AS TIME(7)),
	SimpleProof = DATEADD(ms,DATEDIFF(ms,aTime, bTime),CAST(CAST(0 AS DATETIME) AS DATETIME2))
From myCTE a1
CROSS APPLY (SELECT s_difference = DATEDIFF(second,aTime, bTime)) a
CROSS APPLY (
	SELECT q = CONVERT(VARCHAR(8),DATEADD(second,s_difference,0),108) + '.' 
	+ RIGHT('000000000'+CAST(DATEDIFF(ns,DATEADD(second,s_difference,aTime),bTime) AS VARCHAR),9)
) f;