I looked and can't come up with one.
I think people are reading into the time of the search and the manner it was conducted and draw their own conclusions. The search was not resumed first thing in the morning due to the task of organizing the hundreds of people showing up to volunteer (it had already hit social media by then) and ensuring that you can conduct a proper search with dogs present since you don't want others throwing them off their track.
In addition, searchers cannot simply walk onto private property (which is where the crime scene ended up being at) and start looking around more than they can walk into one's bedroom and start opening drawers. If the owner is not providing consent you might be up a creek unless you get a search warrant.
So, MOO, they were not sitting around waiting for the dogs per se. They were getting organized, they were making sure they were staying out of the dogs' way and getting any relevant approval to go into people's private property that was within the search radius.
MSM article:
UPDATED: Foul play suspected after bodies found along Deer Creek in Delphi; vigil held
Relevant quotes:
"By mid-morning, the downtown Delphi Fire Department became a makeshift command center for volunteers assisting in the search. Crews were being sent out 10 to 12 people at a time to help cover an area of 20 to 25 square miles, Leazenby said."
...
"They had been instructed to stay away from the area where the girls had last been seen because search dogs were out. Authorities told volunteers they didn’t want to chance contaminating the scene.
“At first I couldn’t understand why we weren’t searching near [where they went missing],” said Boucher. “But once they explained it, it made sense.”"
...
"The fields were muddy and the search party was having difficulty contacting property owners to gain access, so the group mainly focused on walking along the edge of the road, peeking into barns and buildings along the way and scanning fields for any sign the girls had been in the area — a piece of clothing, a fresh-looking can or bottle, anything."