Character A is a psychiatrist practicing in the UK in the mid 1960s who plans to kidnap someone. He needs to knock them out temporarily via injection - for a duration say between 30 minutes and 2 hours. So I need a very fast-acting anesthetic (less than a minute between administration and effect), which a psychiatrist would have access to.
I'm having trouble finding something suitable, as most of the information out there doesn't address all the criteria (1960s, rapid-onset, short duration), and I've gotten a bit mixed with sedatives and hypnotics.
Terms searched: general anesthetics, hypnotics, sedatives, intravenous sedation/anesthesia, + 1960s. Also read the Wikipedia page on the history of general anesthesia (very focused on intubation), sedatives, and some pages on individual medications (Fentanyl, Diazepam & Benzodiazepines in general).