NewUserMessage
There's no way to have a hook execute a while after it is triggered, so this cannot be done.
We must find an alternative to this, because it's a waste of time to be forced to give oneself oversight access on all projects where the user talk page has been created (vandals know it and target those wikis, so sometimes we have to change this bits on three different projects to oversight everything). We have a button to oversight things globally, but this does not suppress the user and user talk pages as well. By the way, do you think it will be possible to do this change on the CentralAuth extension ?
I think I will offer those communities a bot script compatible with the extension you wrote, ie using exactly the same MediaWiki messages, so it could be easily moveable. The only way to add a small delay before welcoming is to use a bot, if not doable by any extension.
To stop the extension, should I open a new thread on Bugzilla or simply edit a MediaWiki message ?
Thanks by advance.