Hii!
The Gujarat Secondary Education Board released the exam datesheet for class 12th on 3 February, 2021 on the official website, gsebeservice.com.
You can visit the official website and see the datesheet.
The exams will be conducted from 10 May, 2021 to 25 May, 2021.
The link given below will help you with more information-

https://www.google.com/amp/s/school.careers360.com/articles/gseb-hsc-time-table/amp

Hope this helps.
Good luck!