And, as usual, there are several takes on the answer, but i like this answer. it has some provenance.
Posted by: CYRXorbust
i asked the SEC this question and this was their response:
The decision to delist a security from an exchange or service is made by the exchange or service, not the SEC. However, the SEC does have the power revoke the registration of a security. In that instance, I can't give you a time frame. That is decided on a case-by-case basis.
hope this helps