The very last day is tear down day, so that morning is when you get to hear the systems at their most good or bad state, depending. If you go the day before and stay over night for the next morning the sales hype will be on it's last leg and you can get the designer to play something outside of his or hers pre-pick music. That gives you a day and a half to get to know the sound not just getting caught up in the shuffle. The first day of any show is a waste of time. No way are the systems any where near settled. In fact, if you read a raved review of the sound on the first day, look to see if those products are being advertised in that particular magazine. It takes months before a system starts to gel, so don't think that the sound you are getting at an audio show is anything remotely like the real sound of the system. Many audiophiles use the "show" sound as a reference. Well, back when there were 2 or 3 days of setup before a show, and when the hip designers played music all night long and invited you to join in, that was a real audio show. Todays shows are a cutout version of those days.
My advice is look for simplicity of setup. There are some folks who really know how to do a show, and after you've been to a few of them you start to zone in on their expertise. I could give you a list of names but then others would get mad at me. If your a gear junky I have zero advice for you. I have never been interested in gear, only sound. And I have never been interested in show sound, only those few magical people who somehow pull of miracles and pass a lie detector test. 90% of the companies there are after your money. 10% of the designers there are pure playback Gods. happy hunting and always make the show, your show
Michael Green