Dear Student ,

In case of any competitive / Entrance exam , you are not allowed to attend your exam later instead of the original date of exam that is allotted to you.

After your submission of application , i.e.. the admit card has been generated with the details of final exam date , venue with time .

Well, in case of any school/ college / institutional exam(not board exam ).. any medical issues can be considered by your institute authority, in that case you need to contact with them personally to  give you another chance for allowing to appear for the exam later !

Hope you understand !