"It is two o'clock now."
Translation:Сейчас два часа.
You are right! It still works for about 11:00 till 17:00 period of time. Beyond the limits or near the boundaries it would be necessary to clarify whether "6 часов утра" or "6 часов вечера" for examples. I think, the boundaries values depend on time, when people used to wake up. So, for party person, "два часа" is 2 a.m.