While 20 Time is a structured, methodical project, Genius Hour allows more flexibility to the concept of 20 Time.
Genius Hour allows students to spend one hour per week working on independent study of their choice. The final outcome is different for every teacher. For instance, Joy Kirr (see her contact info in Genius Hour Community) integrates 20 Time with reading. Some teachers ask students to create a focus or essential question that they try to answer. It may be that you allow your students to research whatever is on their minds for that day. Some teachers allow students to present findings at any point in the semester and then begin a new project while some teachers have specific rubrics.
Genius Hour fulfills that autonomous, inquiry-based learning that we are trying so desperately to instill into our students today. If you do not want to do a full-on project, if your students cannot handle a large project, or if you simply want to try a few weeks of Genius Hour to see what it looks like, find your own version and create autonomous learning in your classroom!