This is a great question...but I really can't say. I've only tripped about four or five times, and all but one of those was during the day. (Mostly because I only had two days planned out each time, for the trip and then recovery, and didn't want to throw off my sleep schedule.) The time I tripped at night was my first time, and I was inside the whole time, so I can't really give any input there. One day I will trip at night again to get the full experience, now that I understand acid better, but until then, I feel I can only really talk about day tripping.
Which is great! I feel like the sun's vibrancy combined with the color-sharpening effects of acid makes the outside world beautiful while tripping. Each time I have tripped during the day I have taken a nice walk down to the river for the sole purpose of appreciating nature, and I love it. Also, it's enjoyable to use natural light when sitting inside, rather than fluorescent lighting. Granted, since tripping on acid lasts so long, and I usually don't start until 10 or 11 AM, it often gets dark outside while I'm tripping. But when the sun goes down, I take that as my cue to go indoors and do things there (often using blacklights and listening to music).
Maybe one day I'll go outside at night while tripping, but I don't know if that's the best idea in my town. Don't really live in a big city, though, so walking around at night might be suspicious and give greater risk to a run-in with the cops or shady types of people - both situations would be bad for a trip...