Not quite right there, Judicious. Perhaps a popular misconception with all these CSI shows on TV, which have almost nothing to do with real world forensics.
Rigor mortis (i.e.the stiffening) sets on in 3-4 hours usually, reaches a maximum at about 12 hours, then passes off (from top to bottom incidentally) over the next 24-48 hours.
Livor mortis, to which I referred in the post above, is the gravitational pooling of blood and blood pigments, indicating the position that the body had been lying in. For example, if a body is lying on its back, then the livor mortis (a.k.a. lividity) shows up as a blueish-purplish blotchy discolouration on the bit that was lowest - the back. The limbs reflect this also. So you can assess what position a body was in due to the position of the livor mortis - which is what I think the prosecution were referring to in the bail hearing. They were suggesting that due to the livor mortis, the body would appear to have been in the same position since shortly after death (i.e 3-4 hours) as the livor mortis would indicate no change in that position.
Livor mortis stays put, whereas rigor mortis fades away over 48-72 hours post mortem. But both take 3-4 hours to set in. It's not instantaneous, even if the victim is high on adrenaline fighting for their life. The main factor that can vary the onset time is the ambient temperature - which would have been taken into account in Allison's case.
Hope that makes sense...