Actually, you don't need a training class. You can search information online and do it at home. There is a lot of good information in the QZZN forum, and others also put the internal information of the training course on the forum and can download it.

After the written test and interview, you can take part in the study class if you can, because there are simulation exercises, which can exercise your confidence and courage.

General/kloc-exam around 0/2 months.