If you're using 24 hour time in English, the proper way to say it is "It's twenty hundred hours", or "It's twenty", otherwise you'd say "it's eight o' clock in the evening" or "it's eight pm".
A suggestion for the English translation; it seems like you’re using military time so the phrase “it’s 20 hundred hours” is a more fluid way of talking about time in this way.
Twenty o'clock has now been removed.
Twenty o'clock??? In English the clock a time can be "of" only goes up to 12.
As others have pointed out, "twenty o'clock" is not considered proper English, at least when telling time on this planet.