it would be a great if scheduled workbooks are executed at that time zone which selected in Advanced Scheduling Options.
Actually a reportBuilder workbook is executed at data center localtime, e.g if your data center is in San Diego you have GMT-9. If you are using Excels date and time functions you have to ensure that the scheduling time is late enough that the functions working as intended.
E.g. using Excel TODAY() is 10/06 6 AM (WEST) and 10/05 9 PM (PDT)