> Where no time is specified in the offer, the offeree has a reasonable period of time to accept the offer. After a reasonable period of time expires, the offeree's power to make a contract by accepting the offer "lapses". ... When a seller purports to accept an offer after it has lapsed by the expiration of time, the seller's acceptance is merely a counteroffer and does not create a contract unless that counteroffer is accepted by the buyer.

-- Anderson's Business Law, Formation of Contracts: Offer and Acceptance: Lapse of Time