CREATE OR REPLACE TRIGGER Correct_TimeTible
INSTEAD of Insert ON Timetable1
BEGIN
if  to_char(:new.DATE_BEGIN, 'hh24:mi') >= to_char('9:00', 'hh24:mi') and
to_char(:new.DATE_BEGIN, 'hh24:mi') <= to_char('16.30', 'hh24:mi')
then Insert into Timetable values (:new.ID_TIMETABLE,:new.ID_SUBJECT,:new.ID_TEACHER,:new.ID_TYPE,:new.DATE_BEGIN);
ELSE dbms_output.put_line('Incorrected time');
end if;
END;

CREATE TABLE  "TIMETABLE"
(   "ID_TIMETABLE" NUMBER,
"ID_SUBJECT" NUMBER,
"ID_TEACHER" NUMBER,
"ID_TYPE" NUMBER,
"DATE_BEGIN" DATE,
 CONSTRAINT "TIMETABLE_PK" PRIMARY KEY ("ID_TIMETABLE") ENABLE,
 CONSTRAINT "SUB_TIME_FK" FOREIGN KEY ("ID_SUBJECT")
  REFERENCES  "SUBJECT" ("ID_SUBJECT") ENABLE,
 CONSTRAINT "TEACH_TIME_FK" FOREIGN KEY ("ID_TEACHER")
  REFERENCES  "TEACHER" ("ID_TEACHER") ENABLE,
 CONSTRAINT "TYPE_TIME_FK" FOREIGN KEY ("ID_TYPE")
  REFERENCES  "TYPE_SUBJECT" ("ID_TYPE") ENABLE
)
/

insert into Timetable1 (ID_TIMETABLE,ID_SUBJECT,ID_TEACHER,ID_TYPE,DATE_BEGIN)
values (SEQ_TIMETABLE.nextval,'1','3','1',to_date('20.05.2018 15:00','dd.mm.yyyy hh24:mi')
);

if  to_char(:new.date_begin, 'hh24mi') >= '0900' and
    to_char(:new.date_begin, 'hh24mi') <= '1630'
then
    ...