-Snipped for very important bolded content-
I think this ends all the speculation of Barbara going missing at noon, and Robert not calling 911 until 3.36.
The sister of our VI clearly says here Robert calling at noon, police arriving, two hours later: at 2.00.
Two hours between his call and the police arriving.
If we just take over the part of Robert getting worried at noon, and add to that that he called 911 at 3.36 it is mixing up two versions.
It would be the same as taking over the part Robert calling police at noon, and then add to that Barbara went missing at 2.30, claiming how could he report her missing hours before she was actually missing etc.
In Robert's version to his niece, or in the recollection of his niece, he called 911 at noon, and police arrived at 2.00.
So he did not let 2 or 3 hours go by before calling 911. IMO