The name timestamp is very badly chosen. It is a binary number, not an actual date.
Given the issues with timestamp, wouldn't it be easier to just use an IDENTITY column? This simply increments for every new record.
You can have gaps (if transactions fail for example), but as long as you don't mess with the column new values have always bigger values than the previous ones and duplicates do not occur.
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MCSE Business Intelligence - Microsoft Data Platform MVP