You may be correct in that finding JJ came first, but I would think that with the amount of personel there and the intel they had, that they were working on both spots at the same time. JJ was easier and quicker to recover considering the body was intact. Although the property isn't that big, JJ's burial spot was in the back of the property. Chad was sitting in his daughter's driveway and not knowing the lay of the land or Chad's vantage point, he may not have been able to clearly see JJ's spot. It's also possible that his line of sight may have been blocked by equipment and/or screening.
Tylee's location was much more centered in the property and much closer to the road and as we know, her remains were much more strewn about the area. It would have taken a lot more time with digging, sifting, and sorting out human bones from animal bones. Chad sat there for a while before he took off. On an earlier thread someone mentioned that he could have been Googling lawyers but there may have been a bit of sarcasm in that thread.
Maybe some of this can make sense but it's just my guess. Bottom line is that when he figured out he was busted, he tried to run.