It really depends where I'm going. The nearest show to me is about 3 hrs, the farthest is pushing 8.5 hours. Because I show in eventing, the venues in my area are few and far in between. I'll give you a run of the show I attend most often.
Getting Ready to leave (wrapping, loading, hitching, etc; there and back) = 1hr x 2 = 2 hrs
Travel (there and back) = 3.5 hrs x 2 = 7 hrs
Actual showing differs, tbh. Since events don't really have "classes" per say. I mean, you register for your division, then you're placed in a subset of the class if there are a lot of people entered. For example, I might be showing Novice level, but be in Novice Section B for my riding class because there are so many entrants in my division. Then your dressage and stadium are usually on Saturday, with cross country on Sunday, so it's kind of hard to give an exact time table. Generally I warm up for dressage for about 45 minutes, depending onthe horse I'm riding. The test itself is about 6-7 minutes, then I head back to the barn to give the horse a break (anywhere from 10 minutes to an hour depending on when stadium starts) then change tack and head off to warm up for stadium, usually about 20 minutes, then a 1.5 minute course, and I'm done until the next day.
I'm actually at the venue itself from early Friday afternoon until Sunday midmorning or afternoon, depending on my cross country time. So we have to get a hotel every time I go show.
"Always be yourself. Unless you can be a unicorn. Then, always be a unicorn."