The sentence structure is correct. If you ask someone if they "can" do something, you are asking if they are able to do it, though many people do use "can" to make a request in common spoken English. The correct word to use in this case would be, "Will". Also, it should be capitalized as the first word in a sentence. "Melbourne" should also be capitalized because it is a proper noun. There should be a space between "3" and "pm". When making a direct quote we use (") instead of ('), unless it is a quote inside another quote. So, the sentence should look like this. "Will you please call me before 3 pm in Melbourne time?" Anyone who knows the English language would have understood your sentence the way you wrote it.

Almost. You don't need the preposition. "Can you please call me before 3pm Melbourne time?"

yes.