The amount of money is defined and can be bounded.  So can the amount of work, in the sense that what is expected to be accomplished by the end of the week can be defined and described. 

The essence of the agreement however in this case is the time schedule, or one week.  Beyond that week, no further property interest exists for either man in the agreement, which has ended - providing of course that each man has fulfilled his end of the agreement.

Keep in mind that a contract or agreement does NOT create a condition of either party over the other party, or over the property owned by the other party. 

The second man does not own the labor of the first man, who remains in complete ownership of himself, his energies, and his faculties.  The only property in this case is the agreement itself, and this is jointly owned by the two parties to the agreement. 

To take this illustration further, let us say that individual A agrees to pay individual B the sum of $100 for one week's work.

B agrees to perform the work in an agreed-upon manner, adhering to agreed-upon standards of performance and result.

The week passes and the work is done.  Now, does B "own" $100 of A's money?

Not YET.  It is up to A to deliver the money to B, as per the terms of the agreement.  It is not up to B to TAKE it.

Until the money is actually delivered to B, it is still A's money and not B's.  B's property interest is in the agreement, not the money.