Probably quite long, since I would treat each of them with care and respect rather than acting like those fuckboy protagonists. Unless that made them even hornier and more forward?
As long as I can "save" and just replay all of the poor decisions that I made in the past. As long as I only have a few options governing what I say and do to the other characters. I think it would only take as long as it does in the game normally. Of course if it is a sandbox game I would "Quit". Sandbox games are stupid.