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.
On desktop:
- Inside the conversation, click the conversation name at the top.
- Click
Timed Messages. - Set the timer.
- Click
Close.
Anyone in the conversation can change the timer, or turn it off at any time.
Guests in team conversations cannot set or change the timer.
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.