I have to disagree. The guys put Mangum in the car at 12:41. Roberts notices that Mangum doesn't have all her stuff. She goes back for it, doesn't get it, has an argument, calls them some choice racist names, leaves in a huff, yelling and threatening to call police. The cabby pulls up as this is going on, and notices a woman wearing jeans and a sweater coming from the side yard of the house yelling and looking angry. The time it took Roberts to go back, have an argument, and get back in the car is probably 2-3 minutes, so she takes off right about 12:45. They drive away to someplace out of police sight because Roberts, who is running the show, has a warrant out for her arrest, stages the 9-1-1 call at 12:53, and the cops arrive at 12:55. Where they go next is a mystery, then they arrive at Kroger - maybe they went directly there. Maybe Roberts is trying to call Mangum's BF because she really doesn't want to call the cops because of her warrant. Maybe Roberts goes into the store and buys some booze or a Coke, and kicks back deciding what to do.
I think Mangum was drinking before she arrived. Maybe Roberts had a bottle in with her stuff, and drugged Mangum with the plan to rob her later. From the time they were in the bathroom, which would have been about 12:10, until Mangum fell down the steps at 12:30 was just about the time it would take for the drug to start hitting her, and it would have been in full effect in another twenty minutes. If Roberts walked out of the house the second time at about 12:20, leaving Mangum in the bathroom another ten minutes painting her nails, she would have been waiting in the car a full twenty minutes. From what I've seen and heard of her, she's not the good samaritan type who's going to hang around that long. Maybe she was talking on her phone to pass the time while Mangum was looking for her stuff and trying to get the money back from the guys.
Bissey said he heard the "It's only a $100" statement when the guys were in the sideyard talking while one of the others was at the car talking the women into coming back in, so that would have been from about 12:05 to maybe 12:09.