My preference is the morning, getting out of bed at 4 in the morning is no joke, by the time your guests have dragged themselves to the vehicle, their timekeeping is not as good as yours. The Sri Lankan formula 1 driver then drives like a bat out of hell, overtaking on blind bends etc. because he wants to get as close to the front of the queue. When you arrive you sit and wait for the gates to open. Safari time, best to go in the quite time as the peak season is a nightmare. Vehicles pushing a shoving each other to try and get the best views, seems to be an exercise in line waiting and queue jumping.
Anyway the question, most animals are far more active in the cooler morning than the hot afternoon.