Final answer:
The buyer can no longer rescind the offer once they take possession of the residence.
Step-by-step explanation:
According to the given information, if the buyer is unable to take possession of the residence on the agreed date, they have the option to cancel and terminate the agreement by providing written notice to the owner at their last known address. If neither party cancels, the agreement will be prorated and begin on the date of actual possession.
Therefore, the point after which it is no longer possible for a buyer to rescind the offer is when the buyer takes possession of the residence.