10 seconds….that seems like a back injury waiting to happen (if significant loads are being used). IMO much shorter pauses can achieve the desired result (elimination of stretch reflex). If isometric strength is the primary focus 10 seconds might be ok but then you'd want to go without the box.
On the rare occassions that I use box squats I use 20 inch boxes and all of my athletes get below parallel. Much of this issue regarding squat depth and box height depends on how much of your thigh / butt is making contact with the box.