DROP PROCEDURE IF EXISTS mysql.store_time_zone;
DELIMITER |
CREATE PROCEDURE mysql.store_time_zone ()
IF NOT (POSITION('rdsadmin@' IN CURRENT_USER()) = 1) THEN
SET SESSION time_zone = '-3:00';
END IF |
DELIMITER ;
 
GRANT EXECUTE ON PROCEDURE mysql.store_time_zone TO 'user'@'%';
GRANT EXECUTE ON PROCEDURE mysql.store_time_zone TO 'user'@'localhost';

modifique o parametro:
init_connect para CALL mysql.store_time_zone
salve e altere o Parameter Group de sua instancia e efetue o reboot

OBS: lembrando que no horário de verão terá que alterar para -2:00

http://stackoverflow.com/questions/15196385/how-to-set-database-timezone-for-a-aws-rds-instance

DELIMITER |  
CREATE PROCEDURE mysql.store_time_zone ()  
   IF NOT (POSITION('rdsadmin@' IN CURRENT_USER()) = 1) THEN     
       SET SESSION time_zone = '-3:00';  
   END IF 
|
DELIMITER ;
 
GRANT EXECUTE ON PROCEDURE mysql.store_time_zone TO 'user'@'%';
GRANT EXECUTE ON PROCEDURE mysql.store_time_zone TO 'user'@'localhost';

$ rds-modify-db-parameter-group PARAMGROUP --parameters "name=init_connect, value='CALL mysql.store_time_zone', method=immediate"