It depends when you go and whether there's an event. I've always managed to walk in and get situated immediately - only a brief wait when going with a group. If there are enough drivers, there are waits for the track itself.
Saturdays are sometimes busy. Tuesday and Wednesday usually not. After 8pm it is even less busy.
I have had the same experience as Chris. It is not too long based on your arrival, call ahead and find out what's going on. If you wait, they have a full bar and you can order some food.
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