This might help: Reference: https://www.investopedia.com/terms/1/8-k.asp Based on the purpose of the 8K, I would say they have to report buy backs of their stock via an 8K to the SEC. They would have 4 business days to do it:
"..What Is an 8-K? An 8-K is a report of unscheduled material events or corporate changes at a company that could be of importance to the shareholders or the Securities and Exchange Commission (SEC). Also known as a Form 8-K, the report notifies the public of events reported including acquisition, bankruptcy, resignation of directors, or a change in the fiscal year..."
"...Companies have four business days to file an 8-K for most specified items..."
"...Financial information disclosure requirements include the completion of an acquisition, changes in the financial condition of an entity, disposal activities, and material impairments. The SEC mandates filing an 8-K for delisting of stock, failure to meet listing standards, unregistered sales of securities, and material modifications to shareholder rights..."
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