If it is the former closing then this will, once again, be an indication of an experienced interviewer. Their controlling of the interview stems from a variety of factors. They don't want to waste anybody's time (particularly their own), they know exactly what they want to achieve from the exchange of information and they have sufficient social skills to prevent people feeling uncomfortable.
It will become clear to you that the interview is at an end, either through the interviewer's actions or through their politely telling you so. Usually the lead interviewer will do most of the talking from now on. Now is not the time to try and assert yourself. You should rather take a reactive role and just be as polite and positive as you make your way out of the interview venue.
The lead interviewer or somebody designated by them will escort you back to Reception. If you won't be seeing the rest of the interviewers as you leave, be sure to shake their hands and to thank them for their time. Don't forget to smile as you say this.