It depends in the beginning a lot because you'll have to do marketing, websites, answer phone calls book classes, paper work, write waivers, etc. Once you get a lot of that stuff done it's just answering emails, preparing a syllabus (if you didn't in the beginning or have a class in which it changes up every week) regular website updates but mostly it's talking to clients and signing them up for classes. A couple times a month you'll have to write checks to your employees...once a month write bills...it's as much work as you make it.
Size matters too, the bigger the studio, the bigger your headache, the more people working for you, the more issues you might have.
My boss runs 2 locations, teaches, practices, manages both sets of instructors and has 2 little guys and she makes it all work with a smile on her face. Not that it's easy or anything but with some organization and a lot of love - it can work out.