Hi murat 'is it 2.30?' is a simple question - 'what time is it now? 2.30?' 'is it 2.30 yet?' is also a question, but with anticipation. To put in a longer format: 'I am hoping that the time has reached 2.30. Well, am I right?' Another example of the same use: 'Is it time to go home?' or 'Is it time go to home yet?'

To me is it 2:30? is like you weren't aware of the time and then you ask casually OR someone just told you the time and you're surprised it's that late OR maybe you are also waiting for it to be 2:30 but it sounds casual like if you don't care that much. Is it 2:30 yet? is like you are waiting for it to be 2:30 and are emphasizing it , maybe because you have to do something important or something will happen at that hour.

u see, the first phrase is just the statement of fact, that it is 2:30. it may be the answer to the simle question "what time is it?" the second one has the shade of surprise. we may continue: "really? is it just 2:30? i expected it was already 4:00!"