At least one of the vehicles was hung up on the embankment, so it would have taken a while (3 hours, though?) to get the materials to leverage it over. I can't remember when they actually went to the hardware store.
I think Monique could have been forced back into her vehicle after she let out the dog, and Pat was probably ambushed at the gate. My hunch is that the phones were in pockets, or in the vehicles, and one of them received a call or text notification after they reached the vehicle dumping point. That clued them in to search both vehicles.