More important than the amount of time you spend there, I think, is the depth of your experience. For that reason, I'd strongly recommend joining a group with a guide. You can reserve a space on an English-speaking guided tour on the website.

There are many guided tours leaving from Krakow, but they vary in quality. But if you join one of the groups led by the on-site guides, I'm sure your experience will be as meaningful as it was for me.