With a little modification this is working. I am having issues when there are more than two lines for each barcode and I think that I have some data that is incorrect. Here is the sql I am using now.
I think I will need to do some scrubbing before determining the MTBF. I really appreciate the help with this.
SELECT DISTINCT t1.BarCode, DateDiff("d",[t1].[Date_Warranty],[t2].[Date_Ent]) AS DateDifference
FROM tbl_MTBF_Multiple_Entries AS t1 INNER JOIN tbl_MTBF_Multiple_Entries AS t2 ON t1.BarCode = t2.BarCode
WHERE (((t1.RA_Num)<>[t2].[RA_Num]) AND ((t2.Date_Ent)>=[t1].[Date_Warranty]));