I've been meaning to ask about this.
Presumably messages are delivered on the next block, so 1-2 minutes on average?
When instant transactions come in, will messaging be instant?
Great use case for NXT, anyway.
I think they said that they don't use the blockchain to send the messages. Even if they did, messages can be delivered in a few seconds, because there is no reason to wait for confirmations. When receiving coins you have to watch out for double spends. There is no such concern when receiving a message. An exception could be when your counterparty makes a promise or something like that in his message, and you want to be sure that it is recorded on the blockchain before you proceed.