Way Back Machine Please!

I don't understand the concept of play dates.  Play date is scheduled.  At my house I get it, at their house I don't.  There doesn't seem to be a protocol.  Do I stay with her?  Can I leave and do other things? Should I leave and do other things?  You know?  Do they want me to stay?  Do they not?   What is the appropriate length of time for a play date?  When I was a kid we just went out and played with the neighborhood kids.   If there were fights or problems we went home.  We worked it out in time and did fine. If you lived farther away, your mom dropped you off and told the other mom when she'd pick you up and there you had it.  Why isn't that so easy anymore?  I wish I could get in Mr. Peadbody's way-back machine and take my daughter back to the 70's when life made much more sense.