Total speculation, but I think the texts were manually typed and sent by the person in Idaho, rather than scheduled to be sent at a specified time. Even if was not trying to cover up a murder and just needed to send a very, very important message to my boss, I would be completely freaked out about scheduling it and then not having the phone in my possession to see if it sent. Or most important, not being able to see what the response to my text said. Obviously PF would be getting the message to himself to know if it worked. But if it didn't send for some reason, then would he do? Jmo, but I think a person was texting from Kelsey's phone. I also think that person scanned what other messages were received and maybe the knowledge gained from reading those texts helped ward off any growing concern about where Kelsey may be. Where damage control or deflection to any worried friends or family had to be made. (Just my own random thoughts.)
From the police chief's last press conference, it sounds like they must have a lot of phone data from various people to piece an electronic trail together.