Oracle 11g varchar2 datatype with date and time as YYYY/MM/DD-HH24:MI:SS:FF3
First you need to convert it to TIMESTAMP datatype (because DATE type does not handle fractions of second). Then you can truncate it to date for example:

alter session set nls_date_format='YYYY-MM-DD HH24:MI:SS';

with data as (select '2012/09/06-21:17:30:019' as lastupdate from dual)
select 
  trunc(to_timestamp(lastupdate, 'YYYY/MM/DD-HH24:MI:SS:FF3')) date_only,
  trunc(to_timestamp(lastupdate, 'YYYY/MM/DD-HH24:MI:SS:FF3')) + 30 date_only_30
from data;

DATE_ONLY           DATE_ONLY_30
------------------- -------------------
2012-09-06 00:00:00 2012-10-06 00:00:00