California Code, Revenue and Taxation Code - RTC § 12255

The commissioner, for good cause shown, may extend for not to exceed 10 days the time for making a prepayment.  The extension may be granted at any time, provided that a request therefor is filed with the commissioner within or prior to the period for which the extension may be granted.  Interest at the rate prescribed by Section 12631 shall be paid for the period of time for which the extension is granted.