Maximum strength should be trained under 20 seconds as well, Charles Poliquin recommends around 10 seconds for strength training. What's the truth?
Exactly how much would a 30 second eccentric movement "significantly lesson" the possibility of injury compared to 10 or 20 seconds movement. That is splitting hairs.
Is the longer the time under tension the more it gravitates to strength endurance?
Ian King sees strength being developed with sets under 20 seconds, hypertrophy with Time Under Tension Times of 20-40 seconds and strength endurance 40-70 seconds.