event A: 1990 May 23, 12:33:41 UT
 event B: 1998 May 23, 12:33:41 UT


Between A and B are

   8 years          8 * 365 * 24 * 3600  =  252,288,000  seconds


   2 leap days            2 * 24 * 3600  =      172,800  seconds
     (1992,1996)     

   6 leap seconds                     6  =            6  seconds
     (1990,1992,1993,1994,1995,1997)

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      total                              252,460,806  seconds