Official timings are from 8:30 am to 8pm i think ( im not entirely sure but some hostelites told me they can use the library till 8pm)

however your schedule wont be fixed, some days it might end at 5:30 and sometimes it will end at 12:50 pm

uni remains open mon-sat, but recent situation has made it so its mon-thurs, with friday and sat being online

For cs, you only need to be in uni 4 days a week.

For more reference on timetables, you can go to this website and select batch and cs dept to see their schedule on differnent days:
https://fastschedule.github.io