I recall it being reported that the police think she may have been killed as early as 8pm but I think it was later, after the girls went to bed, maybe somewhere between 9 and 10 pm, though that is just my theory.
An argument may have commenced as early as 8pm. (Left the hairdresser 6.30pm)
IMO The killing was not as easy as expected. And things didn't go according to plan.
Firstly it appears Allison put up one hell of a fight. That wasn't supposed to be part of the script.
So the actual killing may have become somewhat protracted.
(Scraps the dog barking like crazy was probably spot on, but there hasn't been an actual time supplied.)
It has been my thoughts that Allison was deceased between 9pm and 1.00am. Possibly even MN. Just my thoughts.