Fin. Code, § 7053

(a) The date of investment in a savings account shall be the date of actual receipt by the association of the account or an addition to the account, except that if the association shall so determine, accounts in one or more classifications or additions received by the association on or before a date not later than the 20th day of the month (unless the day determined is not a business day, in which case it may be the next succeeding business day) shall receive interest as if invested on the first day of the month in which the payments were received.

(b) If the association makes a determination under subdivision (a) it also shall determine that payments received subsequent to that determination date shall either receive interest as if invested on the first day of the next succeeding month, or receive interest from the date of actual receipt by the association, except as provided by Section 866.3.