So here's my theory. Just my thinking out loud.
DEC 27, 2010
5:30am SA leaves for work
6:00am'ish SA snaps and leaves work
6:20 BD leaves for work
6:35 SA arrives back in Colorado City. Assumes that HD is still asleep. Goes to the home. Proceeds to abuse (however sick it was) HD. Can't assume how long.
9:30am SA leaves Colorado City to go to Big Spring to mom's house.
Sometime between 10:00-11:00am HD leaves the home to go do dad's house. Then for some reason comes straight back home. (based on a tip not followed up by LE)
2:30pm SA leaves Big Spring.
3:15pm SA goes to the home. HD is mad. Gonna tell. SA is mad. Doesn't want her to. SA subdues HD. Manages to hide her in the car.
4:00pm CD comes home to a locked house (probably not normal). Makes his way into the window where he sees SA ("deer in the headlights") probably cleaning up the mess from the scuffle. In order to not draw attention to himself from SA, CD acts like nothing ever happened.
AFTER 4:00pm SA leaves the home with HD bound in the vehicle. Now has 2 hours to hide or dispose of HD.
6:00pm SA picks BD up from work. SA most likely needs a "fix". They withdraw the money from the ATM to buy whatever is needed.
Return home as if nothing is wrong.
DEC 28, 2010
HD discovered to have not stayed at friends house and is nowhere to be found.
Any argument, deductions of conclusions are welcome. Again, just thinking out loud.