By default, Marten just uses the underlying timeout configuration from the Npgsql connection string. You can though, opt to set a different command timeout per session with this syntax:
public void ConfigureCommandTimeout(IDocumentStore store)
{
// Sets the command timeout for this session to 60 seconds
// The default is 30
using (var session = store.OpenSession(new SessionOptions {Timeout = 60}))
{
}
}