I highly recommend a guide, you will learn and see so much more, especially since they use telescopes and know where the animals feed and nest. It is best if you arrange your guide thru your hotel or house concierge. They know and work with the "certified" guides all year and know that if you are not happy you will come back and let them know. The normal charge is around $45 per person, including the $10 entrance fee, refreshments, your bilingual guide and RT transport from your hotel/house. Kids under 10 yrs or so are usually charged 2x1. Yes, you can bargain with guides at the gate, but you cannot be sure they are certified, they may just be wearing an official looking shirt. (Some are excellent though.). Either way, they usually charge $20-$25 per person, then you pay the $10 entrance fee, the $4-$6 parking (or more for taxis to get there and back), and you have to buy your own refreshments (they sell nothing in the park). So.....if you do the math, it usually ends up easier to just hire a proven guide through your hotel/house. These tours usually have less than 10 persons, or you can pay around $65 pp for a private tour. The tour is about 3 hrs long on the easier trails, as that is what most tourists prefer, but you can stay in the park and continue to explore on your own if you want. In fact, the whole park is doable on your own, but the majority of visitors always comment to me that they were so glad they went with a guide. Also, regarding the hour to go......most people prefer the morning when it is cooler and the animals are more active, but most guides will also do an afternoon tour starting around 12:30pm, so just ask. Enjoy!