Once you are on the session page, you will be able to watch/hear the presentation and participate in chat.
...
This will remove you from the presentation, but you will still be able to watch and interact with chat.
...
...
Interact with attendees
Send to Breakouts
...
If the timer reaches zero, don’t worry! The session does not close. Everyone remains in the session, and the timer begins counting up, showing how much time has passed since the official end of the session.
...
Find the timer above the chat panel.
...
Scroll down to find another timer.
...
Moderate video and audio
Remove Video and Audio from Screen
...