Sunset. We were there a week ago. We got on line at sunset and by the time we actually got on the ride it was already a little too dark to really see the animals. But we did see most of them. I wouldn't go too late unless I did both sunset and dusk. The lions were very active which was amazing. They were up and were "roaring." The male and females were there. It was so cool!
Their roar sounds more like they are trying to roar. The guide told us that the lion's roar used for MGM is actually a tiger because lion's don't have that kind of roar. Then they said a lion's roar can be heard up to five miles away... Sounds contradictory to me but that's what they said.