I recently cloned a database using this Metalink article. It took less than 15 minutes! It's probably more that you need, but it should be useful...
Note:18070.1
Subject:
How to Make a Copy of a Database on the Same Unix Machine
http://metalink.oracle.com/metalink/plsql/ml2_documents.showDocument?p_database_id=NOT&p_id=18070.1