By setting the timer in a group, all messages sent in the conversation will automatically disappear for everyone in the group when the timer runs out.

1. Inside the conversation, select the conversation name at the top.
2. Select  Timed Messages.
3. Set the timer. 
4. Select  Close.

Group admins can change the timer, or turn it off at any time.

The sender will see a timer  to the left of the message, and once expired, the message will be replaced by a scribble  that disappears once the message has been read.

The receiver will see the message with the time  icon. The timer will not start until the message is visible on screen. When the timer runs out, the message disappears.

Timed messages are synced to the receiver's and sender's devices.

Timed Messages are great for many things, but please be aware that the receiver could still take a screenshot or photograph the screen.