If LE arrived faster than he expected, he could easily have told them that he drove up the road to see if he could spot her.
Regardless, he had a lot of time, the way I figure it. It's a less than 2-hour drive to the Kelbaker Rd. location, they left at 8:30, and now we know they stopped for ice briefly at 9. I'd say they arrived around 10:30. They went for a walk - probably 2-3 walks. RT called 911 at 3:36. I'm leaving out the time the photos were taken for now. If the walks ended around noon, he had 3 1/2 hours of unaccounted-for time prior to the 911 call. If they ended around 2, he had over an hour and a half. And they were in a vast, lonely desert; he didn't have to worry too much about being seen.