The half-hour that I put in the information section was just a basic estimation for the whole game when I released version 0.01, that information is irrelevant right now. Once the last girl, Lauren, will be introduce on 0.06 release, each will have roughly 8 - 10 minutes contents (depending how fast you read their dialogues). So you can expect each girls will have another 50 minutes worth of contents minimum when the game will reach it's final release.
Hope that it make more sense.