It seems the police know that this happened on the Friday, even though the neighbour didn't find them and raise the alarm until Saturday morning. That means Ken Walker was lying critically injured for many hours.
I'm wondering if he got into the house while Freda was at the neighbour's house and then she walked back into it. Perhaps she was spoken to at 6.40pm but was too scared to say anything if Ken was being attacked, and then she was killed because she could identify him.
"The charges allege the defendant murdered Mrs Walker on January 14 and attempted to murder Mr Walker on the same date."
https://www.mirror.co.uk/news/uk-news/man-charged-murder-pensioner-86-26020543
"Derbyshire Police appealed for anyone who was in the area on Friday evening to come forward as 'a matter of urgency'.
'Hours of CCTV footage has been downloaded and is being viewed - and it is clear from the images that there are a number of people who walk or drive along Station Road between 4.30pm on Friday and 9am on Saturday.
The force said CCTV footage had pinpointed potential witnesses in the area at the time it is believed the couple were brutally attacked in their own home. [...]
ACC Kirby added: 'We know that Freda visited a neighbour in the late afternoon, leaving the house at around 4.55pm.
'She walked back to her home and then was spoken to at 6.40pm."
Detectives investigating murder of 86-year-old appeal to passers-by on CCTV | Daily Mail Online
I'm wondering if he got into the house while Freda was at the neighbour's house and then she walked back into it. Perhaps she was spoken to at 6.40pm but was too scared to say anything if Ken was being attacked, and then she was killed because she could identify him.
"The charges allege the defendant murdered Mrs Walker on January 14 and attempted to murder Mr Walker on the same date."
https://www.mirror.co.uk/news/uk-news/man-charged-murder-pensioner-86-26020543
"Derbyshire Police appealed for anyone who was in the area on Friday evening to come forward as 'a matter of urgency'.
'Hours of CCTV footage has been downloaded and is being viewed - and it is clear from the images that there are a number of people who walk or drive along Station Road between 4.30pm on Friday and 9am on Saturday.
The force said CCTV footage had pinpointed potential witnesses in the area at the time it is believed the couple were brutally attacked in their own home. [...]
ACC Kirby added: 'We know that Freda visited a neighbour in the late afternoon, leaving the house at around 4.55pm.
'She walked back to her home and then was spoken to at 6.40pm."
Detectives investigating murder of 86-year-old appeal to passers-by on CCTV | Daily Mail Online