It is the time at which the viewership is maximum; say between 8 p.m. to 10 p.m. Prime time concept is related to advertising rates that could be set higher due to a high TRP.
The product advertised during prime time gets maximum audience.
Can we stretch prime time? Channels have tried to extend prime rime to 10.30 p.m. This is suitable for metro viewers who work till late hours and consequently view TV at this hour. Formerly prime time was up to 9.00 p.m. only, but when it is stretched beyond that it increases the ad revenue. The extended prime time slot now is 7.00 p.m. to 10.30 p.m. Expanded prime time means reaching a broad based audience of different viewing patterns.