I think you're going to find that since it's mid-afternoon on a Saturday it's going to be hit-or-miss on attendance. Lots of folks are running errands or doing family things that need to be taken care of that can't be done during the week.
I think maybe do it as a casual meet - if folks are in town and can show up, that's great; if they can't, no biggie. Just post up a reminder mid-to-late in the week to bump it to the top of the thread. I've found that sometimes just a few folks getting together can be just as enjoyable as trying to get everyone in the area in the same spot at the same time.