from which month should i start the Current affair preparation for CSe 2021?
I would suggest complete newspaper reading in max 30 minutes, supplement with any one website daily news (Insights, Civils Daily, IASbaba, etc - but only one) and then do Vision monthly magazines. If you have free time or low productivity time, watch news analysis video like that of Byju or Only IAS.
You should start from Jan 2020 but focus more on magazines from May 2020.