You get the result after 2-2.5 months.
SSB call if you are selected.
Then after about a month you head to the SSB center accoridng to the call.

Now coming to your question about how hard is this Interview process,

Day1 : 
OIR Test (easy it must be) : You have to clear the cut off for this test. The questions are pretty basic and have Verbal, Non Verbal questions. 

PPDT : If you want to clear Day1 Testing process.This is quite a make or break. Screening test is quite easy and will be cleared with minimum effort. PPDT (Picture perception and Discussion Test), tests your presentation and articulation . Hence, it's important you give a good presentation and discussion.
Once you are in, you are assessed for next 4 days on Psychology,GT Activities, Interview.