Cloud SQL for MySQL upgrade takes very long with HA and Enterprise Plus.

[guynir]

We are now considering moving our production to Enterprise Plus.
Therefore, we are testing the Enterprise Plus on a cloned temporary DB.
The new DB is HA and Enterprise Plus, but when doing a minor upgrade, the downtime was 6 minutes!!!

• I have seen the pre-reqs, and they are checked.
  (https://cloud.google.com/sql/docs/mysql/maintenance#prereqs-constraints)
• I've used CLI to do the minor upgrade:
  gcloud sql instances patch my-test-02 --database-version="MYSQL_8_0_39" --project=my-proj
  
  
  Downtime of 6 minutes is not acceptable for production.
  Am I missing something ?