postgresql – Google Cloud SQL Pricing

For R&D matters i need a small postgresql server.
As I am totally naïve to google cloud platform, I don’t understand the way google bill an instance. The VCPUs are typically factured on a sub-second instance time. But I can’t figure what Google means by instance time : is it the time the Vserver is actually “instanciated” i.e the time range during i can request the DB (24h/day) or is it the time used for connexion, request, compute respond, i.e something like a CPU time (few mins/day)?