You need to file an issuer event report no later than one business day following the occurrence of an issuer event. For example, for a stock split, you report the event within one business day after the issuer issues the securities resulting from the stock split. As a preferred practice, you should report the event following the close of markets on the day of the event or before the opening of the markets on the day after the event occurred. See question 3.3.12.
