Need to think about the time frame as well:
- Sunset on July 18 was 8:41 with darkness at around 9:15. Sunrise and sunset times in Grinnell, IA - July 2018
- The time frame LE are seeking info at the red hot spots is between the hours of 5 PM to 10 PM
- Therefore, there were only 45 minutes in darkness during the window of interest
If you think about it, 45 minutes of darkness is not a long time, and that may rule out some scenarios and make others more likely.
As an example it seems unlikely to me that it would leave enough time for Mollie to get picked up one way or another, have a talk, mini-date, or for things to go horribly wrong. Then more time for someone to hide Mollie one way or another, then think about all the consequences and even begin to plan covering a trail then race back to the car wash for clean-up, however long the car wash is open. (Therefore it seems unlikely they want witnesses to a car washing at the car wash.)
I think it also means LE don't believe she is being held near those hotspots (else why only care about them until 10 PM?)
This makes me think LE is after car wash and truck stop sitings for some other reason than a perp is washing away evidence.
So for all of the hotspots, why is 10 pm the latest LE would be interested? Also the perp could only be in one spot at one time. This suggests the window in darkness has to be 15-30 minutes more narrow at some of the hot spots.