So I just created like 70 “black added sequences” to get the right size for my Twixtor effect on all my clips. Hell of a job. But I discovered a little life-hack for next time. For me, the most important difference between Speed/duration and Twixtor in Premiere Pro is the smoothness of slow motion that Twixtor gives.
After you’ve speed/duration’ed your footage.. you can still apply Twixtor, crank up motion sensitivity to 100 and get that smooth slow motion. I can’t spot the difference. If it’s just a quick, nice looking slow motion effect you’re looking for, this might save you a lot of time.