“How long does it take to wake up after knee surgery?”

The answer depends on the type of anesthesia I used. If you received general anesthesia, it might take you anywhere from 5 to 15 minutes to become fully awake. If you received regional anesthesia/epidural anesthesia, you may be awake within two or three minutes.

The terminology “waking up” means different things to the patient as opposed to anesthesiologist. For you, wake up means an awareness of your “self,” and your “environment.” For an anesthesiologist, it means, a return of the lost senses, i.e., hearing, touch, pain, consciousness, swallowing, coughing, etc.

Knee surgery can be done under general, spinal or epidural anesthesia depending on your choice and the preferences of the anesthesiologist and surgeon.
If general anesthesia chosen, you'll wake up immediately after the completion of surgery but you may not remember it.  
Spinal and epidural and aesthetics can be accompanied with either deep or light sedation or no sedation at all.  The amount of sedation that you received, if any, will influence how fast you will be conscious and remember your surroundings.

People wake up in the operating room, or shortly thereafter in the recovery room, after any surgery. Depending on the amount of narcotic used, you may stay sedated for a few hours.

Usually you would have a spinal for your knee surgery as this has significant benefits post operatively. You would then have a little sedation and should wake up fairly quickly after the sedation is stopped. If you have a general anesthesia , you would wake up but still have some residual effects of the medication and would be kept in the recovery room for about 45 minutes or longer.

It all depends on how each individual responds to the medications given. Some need more and some need less. Some patients wake up very quickly and others take a little longer to wake up.