Tonight's session is a variation of the popular 2*20 minutes which is a regular (and productive) feature of many TT / Triathlon training schedules. Each 20-minute block will feature four, one-minute segments above FTP before immediately returning to a tempo effort. Those will proved the 'Twist' to the 'Tempo'... hence the session name.
This will reflect many race situations, where maintaining a very steady power output is simply not feasible, so coping with variability is needed.