ORA-01830: date format picture ends before converting entire input string / Select sum where date query
I think you should not rely on the implicit conversion. It is a bad practice.
Instead you should try like this:
datenum >= to_date('11/26/2013','mm/dd/yyyy')
or like
datenum >= date '2013-09-01'
You can try this:
Select To_date ('15/2/2007 00:00:00', 'DD/MM/YYYY HH24:MI:SS'),
To_date ('28/2/2007 10:12', 'DD/MM/YYYY HH24:MI:SS')
From DUAL;
Source: http://notsyncing.org/2008/02/manipulando-fechas-con-horas-en-plsql-y-sql/