The main thing is that you can have close contact with animals, play and watch slowly, and it takes at most 3 to 4 hours. The park is halfway up the mountain, and it is still a bit cold when you go up the mountain. Generally, you will miss the opposite Omuro Mountain, so you can queue up and spend the whole day.
When entering the mountain in the morning, there are many transportation options. You can take the tram to Ito Station and take a taxi. It is not much more expensive than taking a bus, which saves time. But after 4 pm, it is impossible to get a taxi. You can only take the bus back to Ito to get a tram.
Either live nearby or take a bus to Ito. It seems that there are also tour groups from Tokyo. The round trip journey is at least 6 hours, and you may not be in the mood to play slowly.