Been reading this post for a while now and so I´ll take my chances and risk make a reply topic. I would only talk of how I do it though.
I live in a very hot weather in summer and a fairly cold weather in winter. Now in summer I always water my trees in the morning, usually around 9 or 10 am as the sun is going high since I have them all facing east, so they receive 4 to 5 hours of direct sunlight.
I must say that they are all planted in an organic soil mix, that is because I acquired them past spring and they came like that. I will repot them next spring using a more adequate substrate though. So, right now, the soil never gets completely dry. For instance for my ficus and olive tree (var. sylvestris) I water them every other day, but for my acers I increase the frequency to everyday. I must say that I do not do this based on a schedule, I do it like this because I have observed that this way all of my trees have been doing just fine. Occasionally, when the day is extremely hot I re-water them a little bit around 3 to 4 pm. Also, one more thing that I do every day is that I sprinkle all of them in the morning and then again in the afternoon... this, I must say, seem to please them highly.
As for the winter, I plan to water my olive tree on a weekly basis, and my ficus and acers probably two times a week. Anyway, this is just a plan that I have right now... When winter comes this, of course, might vary accordingly.
Alain