Prime-time is a borrowing from the English language, which can be translated as "peak time", that is that part of the day in which the TV screens are going to the most audience.
Literally the expression "prime time" is translated as "the first (in terms of ratings) time", that is, the most popular for advertisers who need the greatest coverage. Advertising in prime time is much more expensive than in the morning, day and night. When talking about prime time, speech, as a rule, is about time between 19:00 and 22:00, when the majority of the population comes home from work and sits at the TV, like a zombie absorbing the ethereal chewing gum.
Prime time is in the list: Slang