Cal. Rev. & Tax. Code § 19341

(a) Except as provided in subdivisions (b), (c), and (d), if any overpayment of tax is refunded or credited within 90 days after the return is filed, or within 90 days after the last day prescribed for filing the return of tax (determined without regard to any extension of time for filing the return), whichever is later, no interest shall be allowed under Section 19340 on the overpayment.
For the purposes of this section, “overpayment of tax” includes a refund in excess of tax liability as prescribed in subdivision (j) of Section 17053.5.
(b) In the case of returns which set forth no determination or amount of tax liability, or credits other than that allowed under Section 17053.5, and which are filed solely for the purpose of claiming the renter credit, no interest shall be allowed on refunds made within 90 days from the date on which the return is filed, or within 90 days after the last day prescribed for filing the return, whichever is later. This subdivision applies only when communication with the claimant or other verification is necessary to determine entitlement to the claimed credit.
(c) In the case of an individual or fiduciary taxable under Part 10 (commencing with Section 17001), for the 1982 taxable year and each taxable year thereafter, the 90-day time periods specified in subdivision (a) shall be 45 days.
(d) In the case of a return of tax which is filed after the last date prescribed for filing the return (determined with regard to extensions), no interest shall be allowed or paid for any day before the date on which the return is filed.