When exactly do I have to convert my resident savings account to an NRO account after moving abroad?

Under India's FEMA rules enforced by the Reserve Bank of India, your resident status changes the moment you leave India for employment or an uncertain-duration stay abroad, and you're expected to redesignate your existing resident accounts as NRO promptly. You cannot legally keep operating a resident savings account once you're a non-resident. Practically, notify your Indian bank soon after you settle in the US; they'll convert the account or open a fresh NRO and move balances. Keeping a resident account open as an NRI risks FEMA non-compliance and complicates repatriation later. If you also want to hold new foreign earnings, open an NRE account at the same time so your Indian rupee income (rent, dividends) flows to NRO and your remitted US dollars flow to NRE.