The API is currently the most accurate official data available. It’s caching/when it updates isn’t documented as it could change at any time based on the loads across Twitch. shrug
You could consider opening a uservoice for something “more accurate”
https://twitch.uservoice.com/forums/310213-developers/
It could change or break at any time as it’s not an official/documented endpoint for third parties to use
See