Article 48 of Civil Code

1 - If the offer is made by correspondence, it shall remain open throughout the period specified by the offeror for it to remain open. If the offeror does not specify a period for this, he shall be obliged to keep the offer open throughout the period required by the circumstances for it to reach the offeree, for the offeree to express his view on it, and for acceptance to reach the offeror. 2 - The offer shall lapse if acceptance does not reach the offeror within the reasonable period required by the circumstances, even if issued by the offeree in due time.