Prime temple-visiting time is first thing in the morning. A great way to structure your trip is to plan on arriving in Siam Riap before 4 p.m. to take advantage of the free afternoon visit (the temple complex opens for free every day at 4). If you arrive even earlier in the day, use that day to explore the city or the countryside. The free visit is commonly used to watch the sunset from the top of a temple that overlooks the magnificent Angkor Wat, and is a great way to start your trip.
To maximize your free day, plan on arriving at the entrance into the complex slightly before 4. The most popular thing to do on the first day is to watch the sunset from Phnom Bakheng (all the guides & drivers will know which temple to take you to). The guides will know exactly when the sun will set and what time you should arrive at the temple. In January, we were told to arrive at 5 p.m. When we got there, there were very few people. Fortunately, we secured a great spot and sat and relaxed. Shortly, the temple was crowded with people and there were no good places to sit with a view of the temple – so even though there may be only a few people when you arrive, get a good spot and stay there!