You're not converting a historic date though, you're converting a future date. And that's an inherently uncertain process. It is literally impossible to know wh

You're not converting a historic date though, you're converting a future date. And that's an inherently uncertain process. It is literally impossible to know what UTC time 2021-07-29T15:35:00 IST refers to until it happens. The Indian government is free to redefine IST as they wish, and could choose to do that at 15:34:59.