For the most part, a full day on safari will start with an early-morning wake-up followed by a game drive that starts at sunrise.
After a game drive of around 3 hours or so, you will return to the lodge or camp for breakfast and have some free-time to rest, sleep, go on a guided game walk (where offered).
The afternoon game drive will head out towards the end of the day, and you will usually return to the lodge after dark if you are staying somewhere that allows this.
There are some places where the day might start a little later, and you may have an early breakfast at the lodge or camp before heading out for a full day game drive into a park.
This trends to be more common in East Africa (particularly if you are with a driver guide) and also in national parks where game drives are not allowed out before dawn or after sundown.