How frequently billing section is updated to show usage of mins? is it real time?

The dashboard is not realtime and its cache is variable based on the analytics backend processing loads.

so, how do we know till when billing data is updated? It's crucial for calculating billing and create pricing strategy for diff scenario

I am not sure. But it will be correct when your invoice is created: https://docs.livekit.io/deploy/admin/billing/#downloading-invoices