Around 6 weeks.
Generally someone can get hired at IBM by going through the interview processes, I have hired in IBM through on campus as a Graduate hire. The interview processes consists of three rounds, First round - Aptitude, Second round - Business Email Writing and Third round - Face to Face HR round.
It happened through job portal.
You need to pass the initial interview, written exam, speed test and the final interview for you to be able to get hired.