The time you sleep doesn't affect your dream recall at all. It's the amount of REM cycles you're able to squeeze in. And it becomes more frequent the longer you sleep, so the more hours the better. The reason why we usually sleep at night is because we're not nocturnal creatures. We depend on light to see things clearly. And when our main source of light sets at the evening, it eventually became natural to sleep at night. You could sleep during the day and work during the night for every single day of your life and have the same amount of recall as any other person. (I'm no expert on this, I just picked this up around many different sources across these forums, so please correct me if I'm wrong.)

Well, I'd say what matters most about dream recall is belief and effort, like with any other activity, along with consistency and condition. The reason why I said the last two is because when trying to learn or improve something new, you always have to be consistent with it, else you're going to naturally forget about it and have to refresh yourself when going back. Your current emotional condition can also play a role in dream recall. It varies with everyone, or may not affect someone at all.