Just got back from our trip last week. We went on the safari 3 times. The first was at around 9am, right when we got to the park. There were a decent amount of animals, and they were fairly active, but not super close to us.
We went again around 11-12ish and the cattle were right next to the vehicle, the giraffes were more active and closer, and we thought it was so much better than the first time. Then we went a different day around 2pm and it was the best of all three. Giraffes crossed the road in front of us, and later we had to stop for rhinos. The crossed and then walked right next to the vehicle, only a few feet away. Vultures lined the guide rail we passed. Very neat!
So all three times were good, but our best one was later in the afternoon! I think you are fine no matter what, but definitely don't worry about it being later in the day. The animals do what they want, you never know. As for the cats, the lions were always napping, and the cheetahs were always resting way back in the trees, no difference for us there.