I agree with Adcadet - it depends on the specific area of public health are you inquiring about.
I got a degree in Health Education and Health Behavior (HBHE) in a two year program. Depending on the amount of reading that you would have, I guess I'd spend a few hours per night reading journal articles. Depending on the class, more time was also spent doing group projects (preparing for papers and presentations) - the second year of coursework involved a lot more group work in addition to reading, but overall it wasn't too bad. For my other classes, such as Biostats and Epidemiology (first year requisites) where there were weekly assignments, I'd spend a bit more time on those. My friends who were in Epidemiology and Health Services Admin were always very busy with assignents and constantly studying. Biostats and Environmental folks tended to fall somewhere in between HBHE and the Epi/HSA people.