From your posting (thanks) it would appear that a company should notify MarketWatch as soon as possible of information. Question, is this the official announcement or just notification. Market Watch would determine when the info/announcement is made. And would determine what halt if any be applied.
"NASDAQ MarketWatch assesses company disclosures for materiality and in certain circumstances, may implement a temporary trading halt to allow for even dissemination".
The above is for the NAS - ASX requirements would apply to Australia.
UNS Price at posting:
59.5¢ Sentiment: Hold Disclosure: Held