I have the following process:
Every 20 minutes and for every not completed envelope that I have, I make a listStatus request and immediately after a listRecipients request for the envelope. If an envelope is signed and completed then I make a getDocument request.
After I went through all the envelopes, I wait 20 minutes until I make the next round of requests.
Is this case an API violation?
No, it's not an API violation, but it's not a best practice either. The best way to get status information about an envelope is to use the DocuSign Connect Webhook. This way you don't have to use timers, have delays, or risk API violations. The webhook can be done for a specific envelope, or for the entire account, and it can provide information about the envelope beyond just status.