Disclosure of material information (info that will have an impact on the share price) has to be immediate. They can't even wait until after trading.

However, there are allowances made for keeping confidential information if it would be unduly detrimental to the interests of the company.

For example, "disclosure of information concerning the status of ongoing negotiations would prejudice the successful completion of those negotiations. Disclosure should be made once “concrete information” is available, such as a final decision to proceed with the transaction or, at a later point in time, finalization of the terms of the transaction."

They would have to file a report of this confidential information with the TSX and the TSX would monitor trading closely to see if any information is leaking. If they decide that something is getting out then they will require an immediate notification.

"At any time when Material Information is being withheld from the public in accordance with this section, the Issuer must ensure that such Material Information is kept completely confidential and that persons in possession of such undisclosed Material Information are prohibited from purchasing or selling securities of the Issuer or “tipping” such information until the Material Information is publicly disclosed."

--TSX regulations