Language police to the rescue! :)
"Puu auringonlaskun aikaan" would be the correct (or the clearest, anyway) way to say "Tree at (the time of) sunset" in Finnish.
This time at least all the right words were there, but, as usual, the inflections/cases make the crucial difference. Technically, "aikaan" could be before "auringonlaskun" and it wouldn't be any less correct, but stylistically it's overly poetic for matter-of-fact usage.
thanks for the correction! one of these days, hopefully before the worms eat me, i'll be able to write in finnish as well as a six-year-old! if i do manage this, it'll be at least partially due to your kind guidance.
You know, it probably isn't that difficult to write better than a 6-year-old, as not that many Finnish kids learn to write (to any major degree anyway) until they start school, the year they turn 7. They do start learning their letters in pre-school around age 6, to write their name etc., but they don't deal with things like grammar at that stage. Of course they'll have a bit of a feel for grammar as they hear it all the time, but in the spoken language the grammatical details are often contracted or redacted as this only rarely causes any great misunderstanding between speaker and listener.
It may help with your translation tools (if you use any) to write out the full meaning of your phrase, like I did in my comment above. English is a more condensed language in this way and, as you know, for example the particle "at" can mean a time or a place depending on context, but that meaning will have to be spelled out in Finnish. So writing things out more fully will likely reduce the chance for error. To continue using the above example, the time in the picture "belongs" to the sunset, so it's literally "Tree at sunset's time" in Finnish, and therefore "Tree at the time of sunset", while unnecessarily precise - redundant even - in English, may well get you closer to what you're going for in Finnish.
I hope this wasn't just an incoherent bunch of nonsense, and that it would be of some help and not just confuse you further. Finnish is a fairly tricky language, but at least the rules are consistent, as opposed to English, where the rules are sort of there but most things tend to be exceptions to exceptions to special cases. ;)