Government Code section 11002
(a)
Where the cancellation mark shows both date and time, the remittance shall be deemed received 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 remittance shall be deemed received within the time and date specified when the cancellation mark bears a date on or before which payment is required.
Source:
Section 11002, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=11002.
(accessed May 4, 2025).