Will there be downtime during the Cloud Next upgrade?

Yes. The portion of the upgrade process that requires limited downtime is not expected to exceed 30 minutes in non-production environments, and 5 minutes in production environments. In both cases, the total downtime is proportional to the size of your file system and databases. You can get an estimate of the total time required for these tasks on your applications by initiating a file or database copy between environments in the Cloud Platform user interface or through Cloud API v2.

For customers with larger file systems and databases in their production environments, Acquia utilizes specialized tools to reduce the time to deploy your files and databases to Cloud Next. Those tools make it easier to achieve near-zero downtime for most customer applications, with up to 5 minutes in production environments on the largest applications.