There is a five minute delay on shows. During a recent "live" show I saw a clock on the cooker (they have to have one because if they don't, a lack of knowing the time can lead to total breakdown) and it was five minutes behind the time on my clock at home.
The gaps relate to slander that you and I wouldn't think twice about in the pub: i.e. "I've heard that that celebrity is gay/having an affair/a murderer etc.
Obviously, while we can say what we like in the comfort of our own homes, contestants on BB are not subject to the same rules and obviously don't want to get sued by anyone slandered on air.