Maybe someone has already done it, but I did not see it. I did not finish testing either, so my calculations might be off!
Since the new creaturess were introduced I was able to encounter two of them.
Archaeotherium
Seems to spawn globally all day. I saw her everywhere I went, it was in the day and in the evening.
Meiolania
Seems to spawn in one area only. I did not check what area specifically it was, but I will go out today again and check. The time of day when she spawned was in the evening.
I did not find the third creature. If you have found them somewhere, please tell me and I will edit this post with up to date data! 