I used to drive Safaris (and I miss it :frown:)! As others have said, morning tends to be best for seeing the animals closer and more active. When it gets hotter in the middle of the day, they tend to seek the shade. Later in the day/evening, they start heading off the Reserve for the night.
This is DAK’s signature attraction, so it does have Fastpass. But chances are you probably won’t need it unless, like llama said, you’ll be there during a peak period.
My DAK strategy: I go to Kilimanjaro Safaris first thing and get a Fastpass, no matter how long the standby wait is. Then I jump in the standby line for a morning ride and use my Fastpass later in the day. I like to ride it at least twice because no two safaris are ever the same - the animals make sure of that!