When should my friend file income tax?

Hello,

My friend's income in the period apr 1, 2020 - mar 31, 2021 will be around rs. 875,000 (eight lakh seventy five thousand) only. He is a self employed business professional in information technology segment.

1. When should my friend file income tax returns? before mar 31, 2021 or before dec 31, 2021?
2. Does he need to file advance income tax? if yes, when?
3. If no deduction is applied, what will be the income tax?

Thank you very much.