Mine does exactly that.

If I stand still for 2 seconds she will switch to the pose with her hand on her hip.
If I sit for 2 seconds she will cross her legs and put her hands on her knee. (And if I sit on the ground she will switch to sitting on her knees).

What is the Idle Animation Delay slider set at? that still decides how long it will take before your character changes pose, so if it is set at max it takes a while. (mine is on 2, hence the two second delay before she changes her pose)