The only relevant time is the conditions during that time period. I use the term desert to indicate lack of water for flies to breed. During such a time I would not be surprised to discover that flies don't wander as far and are less likely to find a corpse. I would not be surprised if the animals are what brings the fly's in such circumstances.
Since you seem to be so stuck on getting everyone to acknowledge that the FLIES rode in on a WHITE HORSE (no wrong story) a COYOTE, let's think this through.
First night the body was dumped, COYOTE finds the body and the FLIES leave their seats and go lay eggs on the body. STORY OVER.
You say the COYOTE wouldn't have found the body so quickly. Well, let's see. This PARTICULAR spot was stated to be A FAVORITE ILLEGAL TRASH DUMP for that neighborhood. There was SO MUCH TRASH the FIRE DEPARTMENT had to be called out to clean up the mess. I pretty much guarantee you that the COYOTES knew where the best FOOD SOURCE happened to be. ALL the ANIMALS, and INSECTS for MILES knew that was the SPOT TO EAT.