Do I think he spent more time on the murder? well as I don't believe he did the murder this would all be supposition.
The murderer would have to have met Jodi at some point, we know that a struggle took place(this from expert testimony) the amount of time spent on the struggle could vary dramaticly but I feel about 2-3 mins, he then proceeds to murder her. The throat being slashed around 12-20 times shows a great deal of precision in that he has to avoid himself with the knive and whilst in a frenzied state that becomes more difficult. he then moves the body from where the throat was cut to where the body was discovered and all done so by himself I might add(still not getting blood on himself) a distance if my memory is correct of about 14 feet. He then has to decloth her by cuting the t-shirt and romoving the jeans. Then attempt to tie her up with the jeans by twisting them and securing one hand, doing this to someone who didn't want to be tied would take a while but to a body that is limp is very time consuming. He then has to cut the eyelids very precise and complete other things like repositioning the socks.In all this time he has people in the area and without wanting to draw attention to himslef.
I take it you still think he can complete this in 10 mins?