Not in the old days when it was in Dayton in the early 1980's
If you're one of those types who has to stop at every table and carefully examine everything, you won't make it through in a day.
However, you could do it in one day back at Hara (I did it many times from the early 80s on) and today at Xenia, but as
@BigLebowski noted, you can be rushed. Unless you have a plan (which I do to this day)...
Besides having a shopping list in your head, you kind of developed a technique of moving expeditiously through the flea market scanning back and forth, stopping when something interesting caught your attention; that way you could get through the flea market fairly quickly, and then spend the majority of the day checking out the inside exhibits. I would generally spend about 3-4 hours outside, and another 4-5 hours inside, and didn't really feel as though I'd missed anything. I favored hitting the inside exhibits when it was bright and sunny outside, as that's when most of the herd would be out in the flea market. Don't try to do inside if it's raining outside; you'll never get through the herd of moistened hams.
My single pet peeve about any hamfest, but especially Hamvention? The groups of gomers who would stop in the middle of an aisle to carry on a conversation, thus blocking the aisle almost completely. If you want to gab, there are plenty of places outside the flow of traffic to do it.
Things changed once I started helping out at an exhibitor booth; since you could get in early with your exhibitor badge, I was able to visit the scheduled inside stops on my shopping list easily, without fighting to get through. I don't do the flea market too much anymore unless I have something specific I need to get from a vendor I know is out there; I've got too much stuff already.
