Timeline, based on what we know.
This is based on distance. I think it opens up a discrepancy regarding either when Skyla's mother called or why Grandpa waited as long as he did to look for the girls.
Following is based on:
6/10 mile to the bridge = 3168 approx. 3170 feet
3 mph that average woman walks = 1 mile per 20 minutes = 1/2 mile per 10 minutes =
2640 feet approx 2650 or 265 feet per minute.
2270 feet return from the bridge = 3170 feet to bridge minus 900 feet (300 yds that news reports say the bodies were found from the house).
Girls made it to the bridge and were returning back.
Girls were shot and killed where they were found.
5:00 girls leave
5:01 265 feet from house
5:02 530 feet from house
5:03 795 feet from house
5:04 1060
5:05 1325
5:06 1590
5:07 1955
5:08 2120
5:09 2385
5:10 2650
5:11 2715
5:12 2980
5:13:45 at bridge at approx 3170 feet return home
5:14:45 265 feet from bridge
5:15:45 530 feet from bridge
5:16:45 795 feet from bridge
5:17:45 1060
5:18:45 1325
5:19:45 1590
5:20:45 1955
5:21:21 2120 feet from bridge/900 feet from house. News reports first state girls died between 5:20 and 5:25
Assuming the same rate of speed for grandfather, he must leave the house to look for the girls around 5:26
5:27 265 feet from house
5:28 530 feet
5:29 795
5:29:25 900 feet from house discovers body
He doesn't notice anything at 5:26 when he goes on the road that makes him run or makes him go to the car. So, the crime happens probably only 5 minutes before he takes out after them. Not really enough time for the POI to be dallying by the side of the road after the murders, unless he sees grandpa in the distance and leaves, but grandpa doesn't report anything, and his actions don't really show that he does.
So, if Skyla's mother did really call at 5:08 to see state that she was coming to pick her up, does it really take 16 minutes (5:08 to 5:26) to call the girls and be concerned that they don't answer? I am wondering if there are some slow clocks at Skyla's house and the phone call was closer to either 5:13 or maybe even 10 minutes off and really 5:18, which makes more sense. 5:18 chit chat, 5:20 try to call the girls. No answer. Hang up. Maybe try to call again. 5:22 . Get concerned. grandpa puts on shows or something and heads out at 5:26?