1 - 2 hours, maybe. 4 hours not. I live an hour away and quit going 3 years ago. Previous 8 years bought less than $100 total. If you've got any good stuff to sell you' d probably do well. If you go, get there when doors open...you can see everything twice in 2 hours.....spend the rest of the time BSing or be home for an afternoon nap.
Perhaps it's worth clarifying as there are several shows in Ohio. I can't speak to the one next week, but the Columbus show in June is definitely worth a flight or a day or two drive in my book. As is Iowa Gas of course.
My comments were about the Dayton show. The Columbus show is a whole different animal..... it's like "fly in from the west coast every year" good. Not to be missed if you're really serious about collecting this stuff.