Any guesses as to what it means?
Here’s the translation from my hosting provider’s support folks:
All operations which you need to perform with the domain should be done with 15 minutes interval. It is bounded on synchronization of your DNS zones on our DNS cluster.
In other words, don’t be so slow. I tried again, following the instructions, and received the same error. Once the support team removed the domain from my user account on their end, I was able to try again with success.