Depends if you're doing an academic or research masters (and then if you're writing a report or thesis). An academic masters is doable in an academic year, if you plan carefully and take lots of classes. Anything involving research... a year and half to two years probably. Taking time off during your master's depends on your school, department, how your education is being funded, and if you're doing research for someone. If you're paying your own way and not doing research, then no one is going to care if you take a semester off--but you have to make certain that they'll let you come back without reapplying. If you are doing research and they're paying for your education, then it's something you have to work out with your advisor. A lot of people take time off between their master's and PhD.
