20:00 or 8 p.m. We never say 20 p.m. (or 0800 a.m.) as the a.m. and p.m. are unnecessary. The twenty-four-hour time tells us whether it is morning or afternoon. Also, we usually use a.m. and p.m. in normal conversation. 0800 and 2000 are usually used in timetables (bus, train, etc.), at least in British English. The twenty-four-hour system is also used by the military.

20:00 is used in train and bus timetables. It is also used in the military for planning and is spoken: "at twenty hundred hours." 8PM is the normal way to say it otherwise.

24 hours time ( 0 to 24 hundred hours ) comes only in digital system clocks.. and 12 hour system (AM-PM) comes in both Analog and digital systems.. Here In India All Foreign Tv Channels use 24 hundred hours system ... and Indian Tv channels use 12 hours system (AM-PM)

Am pm is used with time from 1-12. Oposite to 24 hour time. Im not sure if in usa or anywhere else. People dont have 24 hour time. So its 00-12am and 12-00pm. Just remember the time is counter her until 12 and again from begining just adding am or pm to be sure about exact time. So it is different from european 24hou time. 00-12 -am 12-24-pm