Seriously though, the gatekeeper will realize he's being manipulated when emotions come into play, so he should be smart enough to take a break when that happens. And although keeping a friendly AI in captivity is arguably evil, the loyalty of the gatekeeper should be with his own species. The potential downside is so huge that erring on the side of caution can be easily justified: both practically and morally.
You're right: the person playing the gatekeeper has to pay attention for at least the agreed upon 2 hours. The character however is free to zone out, ignore everything, switch the subject, etc, etc.
Seriously though, the gatekeeper will realize he's being manipulated when emotions come into play, so he should be smart enough to take a break when that happens. And although keeping a friendly AI in captivity is arguably evil, the loyalty of the gatekeeper should be with his own species. The potential downside is so huge that erring on the side of caution can be easily justified: both practically and morally.