Spontaneous or planned Mixers?

[SATX*APhi]

I need your help regarding this issue.

One of the fraternities my sisters and I would like to mix with wants to do something spontaneously, not have anything planned in advance. For instance, the social chair of the fraternity called one day and said, "My brothers and I are going to dinner at......tell all of your sisters to meet us there in 30 minutes." Okay, this does not work for me or my sisters! First of all, it will take over 30 minutes to get ahold of all of my sisters. Even if I could get ahold of the girls in time, it does take us time to get ready! Hello!!! Also, some girls work and can't get up and leave work to mix!

How do I go about trying to plan something with these guys? If we do not plan something with them, most likely we are not going to mix with these guys. But like I said, their fraternity is one that my sisters would like to mix with. How should I go about trying to plan something with them if they want to mix spontaneously? Also, how are mixers held at your school? Are they planned or spontaneous? Any and all help would be appreciated!