DATEDIFF(MILLISECOND,TIMESTAMP '1970-01-01 00:00:00',"dt") * 0.001
86400

SUBSTRING(CAST(DATEADD(SECOND,CAST("sec" AS BIGINT),TIMESTAMP '1970-01-01 00:00:00') AS VARCHAR(24)) FROM 1 FOR 19)
1970-01-02 00:00:00