Dear Rounakdixit,

Important dates of JoSAA counseling have been gibven below:

• June 15, 2018 - JoSAA 2018 Registration and Choice Filling Commences
• June 19, 2018 - Round 1 of Mock Allotment
• June 24, 2018 - Round 2 of Mock Allotment
• June 25, 2018 - End of Registration and Choice Filling

Once you have locked your choices , you can't be able to make any further changes.

Know more about choice filling using the link: https://engineering.careers360.com/articles/josaa-registration-and-choice-filling