when do top b schools start their admission process?

Dear Ranjith, most top B schools accept various entrance examinations like CAT, MAT, XAT, SNAP, etc. And each exam has its own exam schedule. So most B schools open their online applications quite ahead of the season. And based on the exam score you want to submit for the Institution, the cut offs will be announced. For example, if there is an Institution that accepts CAT scores, the online applications will be open before the CAT exam is even conducted. But once CAT results have been announced, this college will release its cut off for various Categories. And qualified Candidates can apply online. So it totally depends on the Institution and the score it accepts.