The latest posted message remains atop the website until it is overwritten by someone else.
To overwrite the message, a user must pay the previous cost + 10% in ETH via MetaMask
The new message will remain atop the website
and be tweeted out*. The previous message is gone forever.
All messages go live within 60 seconds of transaction confirmation on the Ethereum network.
*Twitter changed their API settings and I'm pending approval