ART. 1193. Obligations for whose fulfillment a day certain has been fixed, shall be demandable only when that day comes.
Obligations with a resolutory period take effect at once, but terminate upon arrival of the day certain.
A day certain is understood to be that which must necessarily come, although it may not be known when.
If the uncertainty consists in whether the day will come or not, the obligation is conditional, and it shall be regulated by the rules of the preceding Section. (1125a)