You should allow the creator of the chat room to adjust the self-destruct countdown, so that users can choose between 30 mins, 1 hr, 6 hrs, 12 hrs, 24 hrs - and also provide a dialog to confirm the change. Also automatically add entry to the chat that the countdown has changed to self-destruct at [X] time.
I've gone ahead and updated the app so that the lifespan is adjustable to be up-to 24 hours. But to make things less confusing, this is only selectable when the chat is created, it can't be changed afterwards.
You should allow the creator of the chat room to adjust the self-destruct countdown, so that users can choose between 30 mins, 1 hr, 6 hrs, 12 hrs, 24 hrs - and also provide a dialog to confirm the change. Also automatically add entry to the chat that the countdown has changed to self-destruct at [X] time.