Yes you can download the JEE main admit card till the day of the exam it will remain online at the official website of JEE main but to avoid any kind of inconvenience due to any technical issues I would suggest you to download it before hand so that you told not face any difficulty at the time of exam.

Please use the link given below to download the JEE main admit card

https://jeemain.nic.in/jeemainapp/DownloadAdmitCard.htm