Why did the Satanists need to pretend to leave and then wait around for hours to perform the ritual to impregnate Samantha when she was in the house right where they wanted her the entire time?
The bad guys have complete control of the situation, between having a guy patrolling the perimeter to using the power of suggestion to ensure she orders the drugged pizza. No need to jeopardise the situation.
The ritual needed to be performed during the eclipse, so they had to wait for that to happen. If they had just asked her to come over at midnight, she would have see through the ruse. Also they are not good fighters, as shown when Samantha manages to kill two of them and could have offed the third. They needed her to drug herself in order for the plan to work.
