You can do date arithmetic directly in Oracle, using days and fractional days. I don't deal with Oracle servers anymore, so this isn't tested, but the syntax should be:

  select contador, cod_entidad_oim, cod_agr, cod_operacion 
  from mapcom_portext.TR0685002 
  where fch_hor_operacion between sysdate() and (sysdate()-(1/24))
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You can also use the 'interval' syntax: