A 70 minute session with descending sets of intervals above your ftp. This is a bread and butter set for me. If you are doing it right then about three quarters of the way through the 3 minute intervals you should start feeling the finger tips pulsating, and getting a little uncomfortable in your skin. The last couple are usually very painful, but in reality that is where the workout really starts. If it doesn't hurt, then your body was likely already equipped to perform the job you are asking of it, and thus it is at that point that you are finally crossing over into an area where you don't have adequate machinery to perform the job. The big efforts at the end are mainly to ingrain in the body that we do not slow down at the end of the workout, but rather, pickup the effort.