Oracle date format picture ends before converting entire input string

Perhaps you should check NLS_DATE_FORMAT and use the date string conforming the format. Or you can use to_date function within the INSERT statement, like the following:

insert into visit
values(123456, 
       to_date('19-JUN-13', 'dd-mon-yy'),
       to_date('13-AUG-13 12:56 A.M.', 'dd-mon-yyyy hh:mi A.M.'));

Additionally, Oracle DATE stores date and time information together.