Hi.

The full course of Written Examination of NDA is covered in 2 months. The full syllabus of Maths and General ability paper of NDA is covered by providing classes daily in Maths, English, GS etc. for two months. Crash course of Written Examination of NDA is held one month before the examination. If you wish to go there it is of a very good quality institute. Feel free to go there. 

Good luck!