Hello bansika 

JOSAA is a authority which every year conducts counselling for colleges like iits, nits,gftis. 

JOSAA will give you a lot of time and even it will conduct two mock sessions before the original one starts. 

During giving choices to counselling it will give you a lot of time and untill the deadline it will give you option to lock your options and even put on hold. 

If you don't lock your choices it will automatically get locked when the deadline ends and there will be no problem such that the options you keep will get deleted. 

It will automatically lock your choices and keep it as your final entry. 

Thank you