Answer: No, an assignment for consideration is irrevocable
Step-by-step explanation:
The above scenario explains an assignment. An assignment simply occurs when an individual who is regarded as the assignor, transfers benefits to another person who is the assignee.
With regards to the situation in the question, it is not possible for Jared to change his mind and tells Sarah to pay him on May 1st and not Matthew. This is because this is an assignment for consideration which in this situation is irrevocable. The assignment will be deemed ineffective if the assignor doesn't receive consideration for the agreement.