What is the week open for Volatility 75 index
Hi @abutter-acetary-2! Thank you for joining our Deriv Community.
In regards to your query, please note that the Volatility 57 index does not close! 
This is one of the main advantages of our round-the-clock Synthetic Indices, which remain open even on weekends and public holidays, and are not influenced by real-market risks.
You may check out more information about our Synthetic Indices here: Synthetic indices trading | Derived indices | Deriv!
If you have any queries, please don’t hesitate to contact us. Thank you for your understanding!
Why do you update the trading hours monthly?
Because the last time I checked, the new week trading hours for Volatility 75 Index began on Monday to Sunday?
Now, it is from Sunday - Saturday.
What range of trading hours do I use if I want to backtest into previous months since the trading hours might have been adjusted?