rewatisachdeva
It totally depends on the department you are going to join, as it can vary from 3 to 10 months.
There is a process of getting a joining letter after cracking SSC.
After the final result/merit list, the Dossier of the candidate is sent to the particular office for which he is selected. After getting all the dossiers from SSC, the concerned department allocates the zone to the selected candidate and then the dossier is sent to that zonal office. The selected candidate is called there for departmental document verification. And after the required medical test, the Joining letter is issued to that particular candidate.
The whole process varies from department to department. As a Ministry can issue a joining letter in 2-3 months whereas CBIC and CBDT take almost 10 to 12 months.