The placement at all the IITs starts in the first week of December every year and end in the mid-December.
During these days only interviews are conducted by the companies throughout the day and night. The online tests are conducted by the companies during Sep-Dec , based on the performance in these tests companies releases the list of shortlisted candidates and conduct their interviews during placement session.
However, if some students are left unplaced then the placement process resumes in January along with the regular routine of IITs.