I prefer evening. Then it feels like I want intimacy for the sake of being intimate with my partner. When I have some sort of intimacy at night it feels like I'm being intimate because we are both in bed at the same time and why not? Its just not the same. I'm more alert in the evening than I am at night.
There should be an option for any time! I chose mid-day though, which is a bit weird I guess. Sex gets me hungry (in more ways than one~) and I love it when my boyfriend and I have great sex at like 1PM and then make delicious lunch together afterwards. It's great.