I recommend asking specific policy questions to the API policy team through https://support.twitter.com/forms/platform
There is somewhat questionable value in a user tweeting a message on a regular, scheduled basis. But if the content is not spam, the user is fully aware and in control of the content being posted on their behalf, it’s clear to the user how to opt-out, and the app otherwise follows the developer terms of service, then it sounds like something not explicitly against the terms of service.
I’d recommend also reading the [support:76915, title=“automation rules and best practices”] and making sure it complies with those as well.