Are you asking for sprint workouts to help in a 20km TT? You don't need or want to build your NM power to ride a fast 20km TT, work L4(Threshold) and L5(VO2 Max) for a time trial of that length. You're talking about an event at least 25 minutes long, it won't be decided by your top end sprint, neuromuscular power or anaerobic capacity, it'll be decided by your core aerobic fitness and your ability to dig deep into the top end of your aerobic range(VO2 max) towards the end. Work 10 to 20 minute threshold repeats and 3 to 5 minute VO2 max repeats for an event like that. That and work on your start and pacing until you can manage your best steady output for the distance without blowing up.
Good luck,
Dave