I interviewed at schools across the country from where I was living, so I scheduled four in a row. It was not a problem, really. Interview days tend to be fun; the interviewers are usually kind, you get free lunch and sometimes breakfast, and you meet current students. Also, you'll have downtime because it doesn't take all day, so you can relax, rest, and prepare for your next interview by researching the schools.
If you have to travel for interviews, spreading them out is in my opinion a very bad idea, in terms of both extra cost (plane ticket prices are rising) and extra disruption to your life.