We just did the Trek in late June in the early afternoon. We were pretty concerned about the possibility of the summer heat ruining the Trek (animals not out, etc.), but we had talked with friends who had done a similar time (of year and day) before and they said it was not a problem. We were also attracted to the $50 per person discount for post-lunchtime Treks, so we went with it. We had absolutely no problem at all with animals being out of sight. The truck that you're on for the Trek has the ability to stop along the way and look a little closer. We were very pleasantly surprised and ultimately quite happy to have saved $200 for our family of four.
As for tipping, I offered one of our guides a tip, and he refused it, saying they were not allowed to take it. Pretty sure he did not even see how much it was, but simply said he couldn't take it, but was very appreciative of the gesture. I honestly have no idea if every guide would give the same answer. I didn't push the issue and used a little of that same money to buy fake giraffe poop as a snack...as it was during the week that said snack was available - ha!
The snack comment above is spot-on. It is definitely enough for a breakfast, brunch, lunch or heavy snack (whenever you happen to be eating it). As I recall, on the three-hour Trek, the food came after about two hours. Six samplings of different things, along with the bottomless juice as noted. There is also a cold water fountain and bathroom (his and hers) at the "rest stop" out on the savannah, along with lots of binoculars. It started raining right after we stopped to eat, so when we got back on the truck, they gave us all a WDW poncho (ours to keep...not that anybody wants to re-fold, clean or otherwise use a used poncho!). They also gave us a cold "frosty towel" after we trekked through the crocodiles and hippos, as well as a keepsake stainless steel water bottle with the Wild Africa Trek logo.
Perhaps one of the best values of the tour was that all the photos taken on your tour are also included with the cost. We had two guides and when one was talking, the other was taking pictures -- some posed with your family and others of the animals or otherwise candid shots of the group. At the end, you get a code and are able download as many of the shots online as you want.
In short (too late -- sorry!), it ended up being expensive, yes, but a better value than I had originally expected...and definitely worth waiting until one of the last few Treks to get the $50 per person discount.