Revenue and Taxation Code section 2513
(a)
Where the cancellation mark shows both date and time, the application, tax statement or claim for credit or refund shall be deemed filed on the date shown by the cancellation mark and by the time specified by law for that date.(b)
Where the cancellation mark shows only the date, the application, tax statement or claim for credit or refund shall be deemed filed within the time and date specified when the cancellation mark bears a date on or before the specified date of filing.
Source:
Section 2513, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=RTC§ionNum=2513.
(accessed May 9, 2025).