Final answer:
The nurse should reassess the patient's pain 60 minutes after administering acetaminophen with codeine to effectively evaluate the medication's efficacy for the patient's severe headache.
Step-by-step explanation:
The nurse should reassess the patient's pain approximately 60 minutes after administration of acetaminophen and codeine. This timing allows the medications to reach peak effectiveness for relief of the patient's severe headache. Acetaminophen and codeine are used to treat mild to moderate pain, and codeine's effects are typically felt within 30 to 60 minutes after oral administration, with peak effects occurring at around 1 to 1.5 hours. However, for safety and efficacy, assessing pain relief at the one-hour mark is a common practice and provides the nurse with information to make informed decisions about further pain management.