Paradigmus, DFS (Definitive Feasibility Study) is usually a...

Paradigmus, DFS (Definitive Feasibility Study) is usually a complex and detailed assessment which is generally used by management and Banks to determine whether the project is worth continuing to production. It ultimately determines whether the project will create a worthwhile profit if continued to production stage. It would be worthwhile reading this
http://www.rpmglobal.com/wp-content...TE-Minimum-Engineering-Study-Requirements.pdf
As far as how long the DFS takes "How long is a piece of string" the DFS is really a continuation of the PFS (Preliminary Feasibility Study) and as much is forward projection i.e. cost and sale price, a certain + or - percentage is allowed.

In order to ascertain whether the project will be profitable a JORC must first be obtained followed by a complete costing of all items including mining and production cost against the likely future pricing of the product. DRA would have been engaged to complete flow charts and costing of the mine and processing.

With regards to AJM's reporting first a mining study was completed followed by the PFS in March and as previously stated it expects to complete the DFS by the end of the third quarter. However it is not uncommon for the DFS to hit snags due to the use of external contractors and be later than projected completion date.