Gets updated every morning, and once every few hours after that. Usually the margin during the day is almost as much as the first file in the morning. But there are times when the margins can go up drastically intraday if markets suddenly become volatile.
If you are trading at Zerodha, you can track margins here: https://zerodha.com/margin-calculator/Commodity/ or you can use our SPAN calculator: https://zerodha.com/margin-calculator/SPAN/