Is it possible for someone given a double dose of anesthetic to be revived? If so, how long do they have before it's too late?
depends on the person, and how much one dose is to begin with. Anesthetic is something that is sometimes given slowly to determine the dosage needed. It's pain medication, not necessarily knockout drugs.
Firstly a sedative and anesthesia are two different things. Secondly: https://www.scientificamerican.com/article/hidden-dangers-of-going-under/ https://www.asahq.org/whensecondscount/patients%20home/preparing%20for%20surgery/effects%20of%20anesthesia Though I am sure under the absolute worst case (rare) situation you could either kill them or put them in a coma.
It really depends on the drug and its mechanism of action. Different people will also generally respond in various ways based on their body chemistry and composition as well. If you look up a drug you can often see parameters for half life and toxicity information.