Re odor, and it being an issue that fast, perhaps not. It's not instantaneous, and there may have been more than enough time to get her moved without a noticeable odor.
We know that the temp range from 4:53am to 10:53am at McKinney station was 73.0-77.0, and a slight dip to 72.0 for part of that. So it was consistently "around 75" between the time when she most likely was dead in his trunk and when he got back to the gas station at 10:15am.
This website
http://webcache.googleusercontent.c...sic-medicine-smell/+&cd=2&hl=en&ct=clnk&gl=us asked Dr. Lyle (the author of Forensics, A Guide For Writers and Forensics for Dummies) about how fast odor would be appearing with a constant 75 degree temp. His reply was "Under those conditions a faint musty odor would appear in about 24 hours." So we can't say an odor would have forced him to have to get her out of his car before a 7:30 trip to somewhere.
As for daylight, that would certainly be a factor. I certainly understand the pre-5:30 or pre-daylight thinking for when he removed her from his trunk. Possible, of course, you betcha. But for me, not the most likely and here's why I think that.
First, I think he went home for a bit to establish an alibi: ie, go home, act normal, then pretend to go to work and hide her when he should have been at work. In fact, he claimed "I was at work at 8, so I couldn't have been involved," and his use of that false alibi, to me, was a red flag that said to me he felt that was EXACTLY when he needed one.
Second, the fact that he wasn't at work at 8, when he really needed to be acting like all was normal, tells me something MAJOR was being done by him at that time that couldn't wait. A manager, skipping work, he had to have a HUGE HUGE HUGE crisis that couldn't wait, that kept him from going to work and pretending all was normal, and I believe we know what that emergency was..
Daylight means he had to find some place remote, of course, away from people. But there are plenty of areas with lonely deserted roads, so I think he mentally picked a place he had deen or driven past before, and went there.