Each is different, as others have said. Be sure to discuss with potential clients and make sure your plans meet their expectations before agreeing to anything. For example, I sometimes do walks and drop ins in addition to hosting and day care. I also have to drop off and pick up my son from school, but my day care client knows that there are times when I will run out briefly and is okay with that. The fact is, I am home with him the majority of the day, and he isn't left alone long when I do go out. And, even though I may run out for a few mins or so, there is usually someone at home, even if I am not.
My day care basically works like this, I am home except when I need to run out, just as anyone else who works at home or stays at home, so it's comparable to if they were at home with their pet as opposed to it being left alone all day during the work day or in a crate for 8+ hours at a time, like some pets are when their parents go to work.