This is one of the key Rules. The one that can never be broken, at any cost. You must follow this one, if none other. So how do you apply this Rule from a Job Fairy perspective?
You start the close before the recruiter or hiring manager does. You wind up the conversation first. Even if you feel the conversation is coming to an end of its own, you start the close before they can. You say that it's been nice talking to them, visiting them, interviewing with them. You make like you're leaving first.
If the interview is going badly, start the close as soon as possible. Salvage what's left of your dignity. Never try to extend the interview longer and longer, hoping it will start to improve. It never does.
If the interview runs way under the allotted time, then you don't have the skills or personality mix they were looking for. Chalk it up to experience. If it runs way over - and you were not the one prolonging it - then they like you. And like your skills. And want you. This is a good thing.
Just make sure you start the close - and listen for how they respond to it.