How long does it take to recover from a 2.5 hour anesthetic?

Depends: Upon the patient's general medical condition (or pharmacodynamics, how the body metabolizes the drugs) and the drugs used on the patient (pharmacokinetics, how the drugs affect the body: how long their effects last, the interaction between them and the amount required for the stress of the particular surgery). Remember, "bigger" surgeries require higher dosages, and those "last longer.".