Make sure your Account Manager has verified the entitlement is added to your account, and your Cloud user has the appropriate Acquia Migrate: Accelerate permissions assigned. See Step 0 in Using Acquia Migrate Accelerate.
When you have the correct entitlement and permissions, you see Create Migration Environment as one of the options in the Cloud Actions menu.
Cloud Platform generally creates a migration environment within 10-15 minutes. However, this process might take up to an hour or more, depending on the size of the Drupal 7 site’s database and files, and network traffic at that time.
This is an expected behavior. The migration environment needs to generate a new database on all of your environments, which stores the copy of the Drupal 7 database that will be used as the migration source. No other changes are being made to any of your environments. However, the UI does not return control until the migration environment is generated.
The file copy operation in Cloud Next takes longer as compared to Cloud Classic. This occurs because the files are first copied from the production environment to an intermediate ODE environment, and then to a migration environment. After the copy operation is complete, the system deletes the ODE environment, thereby keeping only the migration environment. This additional step in the migration process consumes more time.