About the same as 10 minutes per mile, walking, or standing. If you're out in a clear flat area, you're a target. If you're next to a tree, it's a target and you are too close to a target.
Same rules apply to runners as others w.r.t. lightning.
If the lightning starts up, head for shelter now. Close' is, unfortunately, a very broad range. Count the seconds between stroke and thunder. 5 seconds is 1 mile. That outer range may sound extreme.