The answer entirely depends upon your cardiovascular and respiratory fitness. It also depends upon which trail you take. One is roughly a mile and the other...the more rigorous of the two...is just over 2 miles, but it could feel like 20 if you are not so fit.
Just up and down the main path? 45 minutes to an hour, give or take. Like the gentleman above said, though, there are plenty of connecting paths that lead back to the main path/parking lot, so it largely depends on which way you go.
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