Well people are really gonna want to come after reading your post mez!
I've organised quite a lot of day trips and a few evening meets in the past and I've just put the time, date and location (plus agenda if needed) and then turn up. You always get people saying they'll be there and then not coming (and vice versa) but I always ran the day and/or event as it was listed and that was it!!
If I didn't work saturdays I would have said any of the dates. If it ends up on a saturday then I'll be sorry to miss the meet but it can't be helped.
I guess what I'm saying mez is scratch the vote, just pick a date and people will either like it or lump it!!