In strictest Western etiquette, you are not to use a person's given (first) name until you are invited to do so by that person. It happens all the time, though, but I still find it off-putting when someone I don't know addresses me by my first name as though we've known each other for some time.
Addressing them as "Mr. Smith" or "Ms. Jones" is appropriate if you are making an initial contact. "Dear Sir" or "Dear Madam" is also correct, but "Madam" is sometimes seen negatively, as it implies to some that they are "mature" in age.
To play it completely safe, I would suggest "Good morning," or "Good afternoon." You won't have any chance of accidentally misinterpreting gender, and you still convey a respectful, professional tone. Don't worry about the time zone differences. It is implied that you are speaking from your location's time.