I would think it's pretty much the same as here in the U.S.
Once the DISA answers and the sending fax is sending a CNG tone it should transfer immediately.
Are you sure your fax machine is set to answer immediately.
Maybe the transfer is actually taking place but the fax is set for 5 or 6 rings.
Try calling the fax extension from another extension and se how long it takes to answer.
MrG