760 Omission of date in till pavable after date. Ante-dating and post- dating. Computation of time of payment. Ch. 31. No. 5.] Bills of Exchange. An instrument expressed to be payable on a contingency is not a bill, and the happening of the event does not cure the defect. 12. Where a bill expressed to be payable at a fixed period after date is issued undated, or where the acceptance of a bill payable at a fixed period after sight is undated, any holder may insert therein the true date of issue or acceptance and the bill shall be payable accordingly: Provided that (a) where the holder in good faith and by mistake inserts a wrong date, and () in every case where a wrong date is inserted, if the bill subsequently comes into the hands of a holder in due course, the bill shall not be avoided thereby, but shall operate and be payable as if the date so inserted had been the true date. 13. (1) Where a bill or an acceptance or any indorsement on a bill is dated, the date shall, unless the contrary be proved, be deemed to be the true date of the drawing, acceptance, or indorsement, as the case may be. (2) A bill is not invalid by reason only that it is ante-dated or post-dated, or that it bears date on a Sunday. 14. Where a bill is not payable on demand, the day on which it falls due is determined as follows :— (a) three days, called days of grace, are, in every case where the bill itself does not otherwise provide, added to the time of payment as fixed by the bill, and the bill is due and payable on the last day of grace: Provided that (1) when the last day of grace falls on Sunday, Christmas Day, or Good Friday, the bill is, except in the case hereinafter provided for, due and payable on the preceding business day; (ii) when the last day of grace is a public holiday (other than Christmas Day or Good lriday), or when the last day of grace is a Sunday and the second day of grace is a public holiday, the bill is due and payable on the succeeding business day ;