All active court of appeals judges on the 7th Circuit can participate in deciding whether to grant en banc. Any judge can request an answer to a petition for rehearing and no answer may be filed unless requested. Such a request for an answer is made before a vote as no petition will be granted without requesting an answer first. If one active judge requests a vote after receiving an answer, then every active judge votes on whether to grant. If no active judge requests a vote after a certain amount of time, then the en banc petition is denied without a vote. That certain amount of time varies from circuit to circuit, as does the internal operating procedure. In the 7th Circuit, here is part of Rule 5 of the 7th Circuit internal procedures:
(1) Majority. A simple majority of the voting active judges is required to grant a rehearing en banc.
(2) Time for Voting. Judges are expected to vote within 14 days of the request for a vote or within 14 days of the filing of the answer pursuant to the request for a vote, whichever is later.
(e) Preparation of Order. After the vote is completed, the authoring judge, or the presiding judge of the panel if the author is a visiting judge, will prepare and send to the clerk an appropriate order. Minority positions will be noted in the denial of a petition for rehearing en banc or the denial of a petition for rehearing unless the judges in the minority request otherwise. Minority positions will not be noted in orders granting a rehearing or rehearing en banc unless so requested by the minority judge. An order granting rehearing en banc should specifically state that the original panel's decision is thereby vacated.
(f) Participants in Rehearings En Banc. Only Seventh Circuit active judges and any Seventh Circuit senior judge who was a member of the original panel may participate in rehearings en banc.
(g) Similar Procedures for Hearings En Banc. Similar voting procedures and time limits shall apply for requests for hearings en banc except that a staff attorney may circulate such a request.
(h) Distribution of Petitions. Petitions for rehearing that do not suggest rehearing en banc are distributed only to the panel. Petitions for rehearing en banc are distributed to all judges entitled to vote on the petition.
Obviously, if a judge tells his colleagues that he needs more time before voting then the 14 days can stretch out to more time.