I will provide an alternate explanation for the texts, using a very unlikely scenario.
Dad AS calls BS on a landline immediately after the "going to Alberta" texts. BS asks him to meet him at Nanaimo with the $100 cologne. Ignore what he said in interviews for this scenario.
AS arrives at Nanaimo, but BS and KM are already gone. His next text ( July 12 7:37pm ) show frustration about them taking off early, right after picking up Walmart paychecks, and BS not reimbursing him for the cologne.
He waits until July 13 5pm to allow them to arrive in Alberta, rest, etc. He asks for photos from the Rockies. Now imagine BS calls dad, from "Alberta" based on previous chat, and mentions their next destination.
For this unlikely scenario, I am suggesting that BS told dad where the final destination "there" was, and dad checked the estimated arrival at towns where they could have exchanged texts.
So the next text, Sunday July 14, 12pm, may be when dad thought they would be at some town on their long route. No answer.
The unusual Monday July 15, 5AM text was probably when they should have been in yet another town, but not final destination. That is why he took the chance at 5AM, instead of waiting for them to wake up. Little did he know BS and KM were murdering Lucas/Chynna.
Dad waited out the whole day, because of whatever BS told him they would be doing at the final destination. He sent the final "are you "there" yet" text at 4PM after not hearing back. He knew they lied to him, and didn't want to contact him.