In the physical world, if you enter a room in the middle of a conversation, you can't go back in time and quickly re-hear what the people in the room have said. The same is the case with LiveTalk. You cannot go back in time and listen to the audio from the faculty and other students from before you joined the session.
You can always listen to the recording of the LiveTalk however, and hear everything that was recorded, once the LiveTalk is over.