Difference between ending date of one row and starting date of next row...???

Hi -

I need to create a report (eventaully in SSRS but I'm stuck on the T-SQL portion) that shows the elapsed time between a product's refrigerations (warm time). I was able to get this to work on individual products, but the users will want to view this data for a date range or range of products.

The data looks like...
ID         Row#          RefrigerationStartOn            RefrigerationEndOn
abc      1                  1/1/12 01:00                        1/1/12 02:00
abc      2                  1/1/12 02:30                        1/1/12 04:00
abc      3                  1/1/12 17:05                        1/1/12 18:00
lmn      1                   1/7/12 13:30                        1/7/12 14:00
zyx     1                   1/12/12 10:00                      1/12/12 23:45
zyx     2                   1/13/12 00:50                      1/13/12 14:50

So the separate warm time results would look like....
ID        Warm Time
abc     0:30 (02:00-02:30)
abc     13:05 (04:00-17:05)
lmn      NULL
zyx     1:05 (1/12 23:45 - 1/13 00:50)

Or...if possible...(but trust me I would be happy with the above!) Total warm times....
ID         Warm Time
abc      13:35
lmn       NULL
zyx      1:05

The code and temp tables that worked for an individual product are....
SELECT * INTO TempTableRefrigeration FROM
(
SELECT
      r.ProductID
      , o.ShortName
      , dbo.ConvertToOrgTimeZone(RefrigerationStartOn, o.ID) AS Start
      , dbo.ConvertToOrgTimeZone(RefrigerationEndOn, o.ID) AS [End]
      , ROW_NUMBER() OVER(ORDER BY RefrigerationStartOn ASC) AS RowNumber

FROM
      DCITRAINING.dbo.Referral AS ref JOIN
      DCITRAINING.dbo.Organization AS o On o.ID = ref.ReferringOrganizationID LEFT JOIN
      DCITRAINING.dbo.TissueDonorRefrigeration AS r ON r.PatientID = ref.PatientID JOIN
      TC_MasterPatientData AS p ON p.[PatientID-UID] = r.PatientID
WHERE r.PatientID = 'A0BA4B52-39A7-4439-AC84-4ABD203FD4DC' And (r.Deleted = 0)
) AS DT

/*SECOND Temp table to hold the calculated WITs*/
select * into Temp from (
SELECT
        DateDiff(minute, (select [End] from TempTableRefrigeration WHERE RowNumber = 1),
            (select Start from TempTableRefrigeration WHERE RowNumber = 2)) AS WITFirst
      , DateDiff(minute, (select [End] from TempTableRefrigeration WHERE RowNumber = 2),
            (select Start from TempTableRefrigeration WHERE RowNumber = 3)) AS WITSecond
      , DateDiff(minute, (select isnull([End], 0) from TempTableRefrigeration WHERE RowNumber = 3),
            (select isnull(Start, 0) from TempTableRefrigeration WHERE RowNumber = 4)) AS WITThird
      , DateDiff(minute, (select [End] from TempTableRefrigeration WHERE RowNumber = 4),
            (select Start from TempTableRefrigeration WHERE RowNumber = 5)) AS WITFourth

FROM
TempTableRefrigeration AS r1 JOIN
TC_MasterProductData AS p ON p.[ProductID] = r1.ProductID JOIN
MTData AS t ON t.[ProductID] = r1.ProductID
group by r1.ProductID
) as dt

/*Code used for total Warm Time*/
select WITDeath, WITFirst, WITSecond, WITThird, WITFourth, WITIncision,
SELECT
      CONVERT(VARCHAR, (Sum(ISNULL(WITFirst, 0) + ISNULL(WITSecond, 0) + ISNULL(WITThird, 0) + + ISNULL(WITFourth, 0))/60))
                  +':'+ RIGHT('00' +
                  CONVERT(VARCHAR, (Sum(WITFirst + ISNULL(WITSecond, 0) + ISNULL(WITThird, 0) + + ISNULL(WITFourth, 0))%60)), 2)
 AS TotalWIT
FROM Temp
GROUP BY WITFirst, WITSecond, WITThird, WITFourth

I am happy to use anything to make this work (temp tables, table variables, subqueries, dynamic sql), I just don't know what that would be. Thank you in advance for your time and help with this, and please let me know if I can provide anything else to help work on this!
Jessica