Nechomah – they don’t necessarily go out with them at the same time. In fact, they usually don’t. If you are in America for the summer, there is no reason to do so. You would have a list of a few boys to go out with while you are there, but you wouldn’t actually set up anything before you get there.
What you are talking about is more likely to happen if someone lives somewhere far away from the New York area (like Chicago for example) and comes to New York for the weekend to date. They might set up two dates before they come, one for Thursday night or Friday and one for Motzei Shabbos. I have heard of that, but I’m not sure how common it is – it is a bit nuts. I would imagine that anyone who does that is someone who is a bit older and has already been dating for a while.