Given the information presented today, I would say, if BC did it, 4AM is much more likely. If she had vomited either on her own or from being strangled, it would have cleared the food from her system and any alcohol from her stomach but not the alcohol that was already in her blood.
However, the peak absorption for alcohol is generally recognized as b/w 30-45 minutes. It takes the body 1 hour to metabolize 5 oz of wine or 12oz of beer.
So if she was strangled @midnight when she walked in the door and vomited, it would have only cleared the alcohol she consumed after 11:15-11:30 +/-. JA testified that she and NC both had wine at 5PM, and others noted NC consumed both beer and wine at the party. Others also testified that she was "buzzed" at the party which would indicate a more than marginal BAC.
For her alcohol level to be were the ME found it, it would seem that her body would have needed a longer time to metabolize it unless she stopped drinking at 9-10PM if not earlier. Her body would not have been metabolizing the alcohol after she was killed.