I included time for a quick car wash and vacuum, with the idea that he could and would have done a lot more later.
I included time for him to shower etc, either before or after the gas stop at 10:15.
I don't see him having any intent or follow through to return to wherever he took her - ever.
Net result (my scenario above) is she would have been taken somewhere within a 50-60 minute drive radius. That's a monstrously huge haystack for the little needle that is CM, of course.
I see him going away from population, and driving perhaps until he saw "a place" that he liked. That makes me guess he went N or E (the less populated directions from Allen).
I think he avoided toll roads.
An alternative is that he drove someplace that he had seen, or driven by before, that he had a sense of solitude and a place to hide. But I don't think he would leave her in a place with any actual link to him.
One key is that, in this scenario, it's daylight, so he needs an expectation of a chance to be out of sight with enough time to get her out of his trunk and hidden.
Those are the way I see things, of course. Fits my logic, but who knows.
Some facts for that window, pertaining to 8/30/2014 in McKinney (closest weather records).
sunrise - 6:59
temp from 7:30 to 10:30 - 72 gradually rising to 77
rain - none, and it hadn't rained a drop for 12 days
conditions - mostly cloudy, overcast
ETA - I have found out that QF didn't have any actual knowledge of whether EA's parents were home or not. What he had said: "I thought I read/heard somewhere that it was only EA and CA home that weekend and that their parents were out of town. Again, I don't have a link, just thought that was known information from EA's and/or CA's discussions with investigators." And later he again asked: "Haven't we also established that both were out of town that weekend? Given that it was a holiday weekend, it's likely that they didn't come home until late Sunday or, perhaps, even Monday, the actual Labor Day holiday." Then later he posts simply using the assertion/assumption that they were out of town without any validation. So no actual info, and we still need information or verification that EA wouldn't have bumped into his parents, if he had returned to clean up either before or after 10:15 gas stop.