You've hit the nail on the head. There is no point in sitting...

You've hit the nail on the head. There is no point in sitting over the weekend. And no point in announcing with 15 minutes to go in the session. So announce after the after-market has closed but before the close of business.

The only reason I can think to delay until Sunday is that they other party(s) in the arrangement may want timing issues for a release on Friday their local time.

If nothing is announced by Monday morning then there is nothing to announce. The could, I suppose, announce at market open. But I think that unlikely. Always better to give people time to consider.