I play for "long periods of time" in that I leave my 3DS running almost all the time. I tend to do things in the game parallel to myself irl. When I'm reading, my mayor sits in his reading chair. When I'm watching a show, he's sitting on the couch in front of his TV. When I'm eating a meal, he sits in the dining room. When I'm studying or at uni, he sits at his desk. On an alternate character, I've made my town a Rec Center, which has a gym I put my character in while I'm exercising. I also made a 'grocery store/cafeteria' in the Rec Center out of 7-11 series furniture, which I go to when eating out or shopping...
It's a little weird, I guess, but it amuses me. After I've done my in-game daily 'chores' I just do whatever. Fish a little, talk to villagers, play island games... I rarely grind for bells though. I generally get 50-70k a day just playing normally, selling fossils and whatever bugs/fish I catch naturally. But the way I play AC, I play for like 10 minutes at a time, do something else, a few more minutes, do something else. My 3DS is always in my backpack, so I bring it just about everywhere I go.