There are actually a couple attributes, "night cache" and "recommended at night", and "flashlight required" and "UV light required" might provide additional tips, but I haven't noticed that any of them are used consistently enough to be useful for a search.
I've tried to do a search for night caches and haven't found a way that works very well. The best I've found is to go to some night caches you like and look to see if anyone's put them into a "night cache" bookmark list. If so, you might find a whole bookmark list full of night caches.
The bad news is that the reason you're having trouble finding any is that there just aren't that many of them.
Oh I just found the attributes, the icons on the right side of the page. I will search for those and watch out for bookmarks and lists if I can. Thanks.