Brazil abolished daylight saving by decree in 2019, so Rio de Janeiro stays on UTC−3 and India stays eight and a half hours ahead all year. A Rio morning at 09:00 is 17:30 IST; Rio's 18:00 is 02:30 the next morning in India. Utility updates from your system can go at any hour, but replies need an evening owner on your side.
Rio keeps holidays the rest of Brazil does not. The US government's business travel guide for Brazil lists São Sebastião on 20 January and São Jorge on 23 April as holidays in Rio de Janeiro only, on top of national ones such as Carnival. A promotion timed for the national calendar can land on a city holiday in Rio.
Write Rio's templates in Portuguese (Brazil), code pt_BR, not the European pt_PT. The same guide notes that WhatsApp is the most common way Brazilians communicate by mobile phone, and that English proficiency is low, so an English-only template reaches fewer people than you expect.