California Code, Business and Professions Code - BPC § 22373

(a) Notwithstanding any contractual provision to the contrary, the invention developer and the customer shall each have the right to cancel a contract for invention development services for any reason at any time within seven days of the date the invention developer and the customer sign the contract.  Cancellation shall be effected by written notice mailed or delivered to the invention developer or the customer.  If said notice is mailed, it must be postmarked by midnight of the last day of the cancellation period.  If the notice is delivered, it must be delivered by the end of the invention developer's normal business day.  Within five business days after receipt of such notice of cancellation by the customer, the invention developer shall return to the customer, by mail, all moneys paid and all materials provided by the customer.

(b) The provisions of subdivision (a) shall apply to every contract executed between an invention developer and a customer.  Each such contract shall contain the following statement in 10-point boldface type immediately above the place at which the customer signs the contract:  “The seven-day period during which you may cancel this contract for any reason by mailing or delivering written notice to the invention developer will expire on

If you choose to mail your notice, it must be placed in the United States mail properly addressed first-class postage prepaid and postmarked before midnight of this date.  If you choose to deliver your notice to the invention developer directly, it must be delivered to him by the end of his normal business day on this date.  The invention developer also has the right to cancel this contract by notice similarly mailed or delivered.”