Section 97.507 - Computation of time(a) Unless otherwise stated, any time period scheduled, under the CSAPR NOX Ozone Season Group 1 Trading Program, to begin on the occurrence of an act or event shall begin on the day the act or event occurs.(b) Unless otherwise stated, any time period scheduled, under the CSAPR NOX Ozone Season Group 1 Trading Program, to begin before the occurrence of an act or event shall be computed so that the period ends the day before the act or event occurs.(c) Unless otherwise stated, if the final day of any time period, under the CSAPR NOX Ozone Season Group 1 Trading Program, is not a business day, the time period shall be extended to the next business day.