On January 1, Jack and Jill form a contract under which Jack is to build a house on Jill's land, the work to be completed by July 31. When the house is built, Jill is to pay Jack $400,000. On July 31, Jack announces his completion but unknowingly fails properly to bang one last nail into one last shingle on one corner of the newly built roof. Believing he has done his job, Jack gathers his equipment and leaves. On the morning of August 1, Jill inspects the house and sees a loose shingle. She so advises Jack, who responds, "Well, I've taken all my equipment away, and I have other commitments to fulfill. I can't come back right away to secure one nail in one shingle. I'm sorry. I will be able to return, however, in about ten weeks."

Is Jill obliged to pay Jack the $400,000, as provided by their contract?