The cut-offs vary every year in IISER, so it's quite difficult to make any assumptions. Here are some of the facts:

• General category students should secure a rank below 10,000 while the reserved categories should score within 10,000. 
• Overthinking the required rank will just burden and affect your peace of mind. 
• You can learn new skills such as editing, graphics, coding, or hang out with your friends, and family to refresh yourself, as it provides you some relief from the hectic schedule. 
• It is necessary for you to calm yourself down and meditate to concentrate on your studies. 

You just need to give your best and prepare yourself with precision. Rest will simply fall in place. Do not obsess yourself with rank predictions by different coaching institutes, it is fruitless. You should just be focused and confident.