Those seniors are used to going to appointments with doctors who schedule three patients for the same time, figuring that one or two might not show up (can you call in sick to a doctor appointment?) and they'll be running late anyway.  The first one to sign in is the first one served.  You have to tell your clients that there is a $50 hourly fee for use of lobby chairs.  The ones who don't show up, tell them the first available is May 15.