Final answer:
The nurse should turn off the Pitocin IV when firm contractions last longer than usual.
Step-by-step explanation:
When a nurse palpates a patient's abdomen and identifies a firm contraction lasting 2 1/2 minutes, it indicates that the contractions are lasting longer than usual and may be too intense. In this case, the nurse should turn off the Pitocin IV, as it is likely causing overly strong contractions.