The Red loop alone takes over two hours - more if you take a wrong turn. Bringing a trail map along is highly recommended. The main Red loop exits the park in several places but the blaze color remains the same; when you come to a T-intersection at which all three roads are labeled Red there's no indication which Red is the Red you want. Also, the trail makes a tricky turn at Silver Hill Road, and without a map it's very easy to miss the turn and end up on a residential street.
Adding the Yellow and/or Blue trails, the museum, and the side trails and you could easily spend half a day here.