Commercial Code § 3113

(a) An instrument may be antedated or postdated. The date stated determines the time of payment if the instrument is payable at a fixed period after date. Except as provided in subdivision (c) of Section 4401, an instrument payable on demand is not payable before the date of the instrument.

(b) If an instrument is undated, its date is the date of its issue or, in the case of an unissued instrument, the date it first comes into possession of a holder.