P.R. Laws tit. 31, § 3017
Persons obliged to deliver or to do something are in default from the moment when the creditor demands the fulfilment of their obligation, judicially or extrajudicially.
However, the demand of the creditor, in order that default may exist, shall not be necessary:
(1) If the obligation or law declares it expressly.
(2) If by reason of its nature and circumstances it may appear that the fixing of the period within which the thing was to be delivered or the service rendered was a determinate cause to constitute the obligation.
In mutual obligations none of the persons bound shall incur default if the other does not fulfill or does not submit to properly fulfill what is incumbent upon him. From the time one of the persons obligated fulfills his obligation the default begins for the other party.
History —Civil Code, 1930, § 1053.