As we don't want the database user, which has reporting jobs, to connect the database at working hours, following trigger was used to apply this restriction.
CREATE OR REPLACE TRIGGER SYS.DENY_LOGIN
IF sys_context('USERENV', 'SESSION_USER') = 'REPORT_USER' THEN
IF to_char(SYSDATE, 'hh24') BETWEEN 08 AND 22 THEN
'Sorry, it is not permitted to logon to the DB at this time as this user');