"It is late already, turn off the computer and go home."
Translation:Уже поздно, выключи компьютер и иди домой.
it's a bit hard to explain these things, but we tend to use imperfective verbs in imperatives like that, it kind of shows how we want this action to be happening right now. we can even use the past tense to express imperative and say 'выключил компьютер и пошел домой' as if it has already happened -- but that is rude.
Это уже поздно, выключи компьютер и иди домой. also should be taken as a right answer.