The levels are based on the syllabus of the music school where M. Delcamp teaches. Each level corresponds to one whole year of work. But you may find it takes you a longer or shorter time, depending on your experience and skill.
To access levels D04 to D06, you need to join the 020 group, which you can do after you have posted 20 messages, though these should be reasonably substantial. Please see my previous post, just above yours, for more details.
Classical Guitar Forum.
"Experience is something you don't get until just after you need it." - Steven Wright