As no date limit or validity is written about it BUT it is advisable to make the medical certificate in specified Format available on JoSAA-2020 format with the respective CMO (Chief medical officer) of hospital present with recent date, doctor's sign or stamp or hospital's stamp.You can make it on the day you are asked to .

Hi. The document should be dated after the month of April 2020. The validity of such a certificate is said to be lasted for a period 1 year or so. And there is no such right time to make the medical certificate . You can make it on the day you are asked to .

Hope this helps.